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Life Strategies of Plants: Midterm
University of Guelph BOT*2100
1021
Plant Sciences
Undergraduate 2
11/12/2015

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Term
α-amylase
Definition
An amylase. Released by the aleurone layer of seeds during germination. Initiates the breakdown of the endosperm starches into sugar.
Term
ABC model
Definition
A model for the genetic control of flower development in Arabidopsis. Genes are classified by the worls they affect: classes A, B, and C. Loss of a class results in flowers lacking in the whorls they control. It is difficult to say if this model works for other flowers.
Term
ABCDE model
Definition
A modification of the ABC model in Arabidopsis. Includes class D and E genes. It is difficult to say if this model works for other flowers.
Term
Ability to grow
Definition
An attribute of living things.
Term
Ability to reproduce
Definition
An attribute of living things.
Term
Abscisic acid
Definition
A plant hormone that promotes dormancy.
Term
Abscission
Definition
Separation of the leaf from the stem. Structural and chemcial changes occur in the petiole, forming the abscission zone.
Term
Abcission zone
Definition
The area where the leaf separates from the stem. Has two layers: separation layer and protective layer.
Term
Absorption
Definition
A function of roots. Absorbs water and minerals.
Term
Accessory fruit
Definition
Any fruit that has parts which develop from accessory tissue. Example: apples, pears (the floral tube becomes the major fleshy part).
Term
Accessory tissue
Definition
Tissue that is not part of the carpel which forms the fruit of accessory fruits.
Term
Acetabularia
Definition
A member of Codim. Used in experiments on genetic basis of diffferentiation.
Term
Achene
Definition
An indehiscent, dry simple fruit. Characteristic to buttercups and buckwheat. A small, one-seeded fruit. Seed is attached to the pericarp by the funiculus, and falls off easily. Includes samaras.
Term
Actin
Definition
The protein which forms actin filaments.
Term
Actin filaments
Definition

Microfilaments

A component of the cytoskeleton. Polar structures with a plus and a minus end, composed of actin proteins. 5 - 7 nm in diameter. Some are associated with microtubules. Assembled at certain points in the cell. Occur in bundles in many plant cells. Involved in cell wall deposition, tip growth of pollen tubes, movement of the nucleus during cell division, organelle movement, vesical-mediated secretion, organization of the ER, and cytoplasmic streaming.

Term
Adnation
Definition
When floral parts are united with members of other whorls.
Term
Adventitious roots
Definition
Roots that form from nodes of the stem. May form lateral roots. Occurs in fibrous root systems of monocots.
Term
Aerenchyma
Definition
Parenchyma tissues with large and abundant air-filled intercellular spaces. Found in aquatic and wetland plants.
Term
Aerobic
Definition
Using oxygen.
Term
Aesculus hippocastanum
Definition

Horse chestnut

Does not flower until it is about 25 years old.

Term
After-ripening
Definition
The embryo undergoes complex changed while in the seed. Contributes to embryo-imposed dormancy. Some after-ripening is triggered by cold winter temperatures.
Term
Aggregate fruit
Definition
A type of fruit. The carpel retains its identity in the mature state. The individual matured ovaries are fruitlets.
Term
Air roots
Definition

Pneumatophores

Roots that grow out of water to aerate the root system. Found in plants that grow in swampy habitats.

Term
Albuminous cells
Definition

Strasburger cells

A parenchyma cell which associates with sieve cells of gymnosperms, and performs a role similar to companion cells: keeps the sieve cell alive.

Term
Aleurone
Definition
A thin layer of tissue that surrounds the endosperm. Active in digestion of the endosperm during germination.
Term
Allele
Definition
One of two or more alternative forms of a gene, occupying the same locus on homologous chromosomes. Recessive or dominant.
Term
Alpha-proteobacterium
Definition
The aerobic bacteria from which mitochondria evolved in the endosymbiont theory.
Term
Alternation of Generations
Definition
Includes zygotic, gametic, and sporic meiosis.
Term
Amborella trichopoda
Definition
The oldest flowering plants. Embryo sacs consist of eight cells and nine nuclei; there are three synergids. A shrubby dioecious plant from New Caledonia with small flowers and indistinct petals and sepals. It lacks xylem, and has tracheids.
Term
Amborellaceae
Definition
A basal grade angiosperm. Its only living member is Amborella trichopoda.
Term
Amorphophallus titanum
Definition

Corpse plant

Blooms once every 10 years. Smells like rotting flesh to attract flies. Has a spadix flower.

Term
Ambuchanania
Definition
A rare single species in Sphagnidae found in Tasmania, where it grows as "spots" on wet sands.
Term
Amylase
Definition
An enzyme released in the seed that digests stored starches. Includes α-amylase.
Term
Amyloplast
Definition
Leucoplasts which synthesize starches.
Term
Anaerobic
Definition
Without oxygen.
Term
Analogous structures
Definition
Structures with common function or appearance, but not common evolutionary origin. The result of convergent evolution.
Term
Anaphase
Definition
The third phase of mitosis. The shortest phase of mitosis. Simultaneous separation of sister chromatids at the centromere. Sister chromatids are now called daughter chromosomes. Arms of the chromosomes drag as the kinetochore tubules pull them towards the pole. Kinetochore microtubules shorten by motor proteins and from losing tubulin subunits at the plus ends (kinetochore ends). The spindle assembly checkpoint is at the end of anaphase.
Term
Anaphase I
Definition
The third stage of meiosis I. Homologous chromosomes separate and move towards poles, but centromeres do not separate; sister chromatids remain together.
Term
Anaphase II
Definition
The thid stage of meiosis II. Centromeres separate and chromatids are separated and move to opposite poles.
Term
Anchorage
Definition
A function of roots.
Term
Andreaea
Definition

Granit moss

A genera of Andreaeidae. 100 species of small, blackish-green or dark reddish brown tufted moss which often grow on granite rocks. The protonema and rhizoids hhave two or more rows of cells, rather than one. Capsules are lined by four lines of weaker cells which are split and are sensitive to humidity, opening when dry so that spores are carried away by the wind.

Term
Andreaidae
Definition

Granite moss

A class of moss. There are two genera: Andeaea and Andreaeobryum.

Term
Andreaeobryum
Definition
A single species in Andreaeidae which grows in northwestern Canada and Alaska. Grows on calcareous rocks.
Term
Androecium
Definition

"House of man"

Side branches with modified leaves that hold the antheridia of leafy liverworts.

The stamens of a flower.

Term
Angiosperm
Definition

"Seed vessel"

Flowering plants

A member of spermatophytes. Dominant on earth, and extremely diverse. The gametophyte generation is very reduced. Non-motile sperm are delivered to the egg by the pollen tube. Includes monocots and eudicots. Appeared very suddenly 135 million years ago. Evolved from gnetophytes, but actually gymnosperms and angiosperms are monophyletic.

Term
Angkor Wat
Definition
The capital of an ancient civilization in Cambodia. Roots of the strangling fig tree encapsulate ancient buildings to reach the ground.
Term
Angular
Definition
An organization of collenchyma cells. Thickened at intercellular contact points. Only thick where they touch.
Term
Animal-borne fruits
Definition

Sweet, highly coloured fleshy fruits co-evolved with animals; the majority of fleshy fruits are eaten by vertebrates and the seeds are dispersed by being passed through the digestive tract or being regurgitated. Sometiems partial digestion aids in germination. As the fleshy fruit ripens, it undergoes a rise in sugar, softening, and change in colour.

Many fruits are dispersed by adhering to the fur or feathers of animals. Fruits and/or seeds have hooks, barbs, spines, hairs, or sticky coverings that allow them to be transported attached to the bodies of animals.

Ants disperse with elaiosomes and eat the elaiosome. Up to a third of plant species in some communities are dispersed by ants.

Term
Animalia
Definition
A kingdom within Eukarya. Contains animals.
Term
Annual
Definition
Plants with a life span of one year. The stem is photosynthetic. Includes weeds, wildflowers, garden flowers, and vegetables.
Term
Annual ring
Definition
A growth ring which is formed annually.
Term
Annulus
Definition
A row of specialized cells in the sporangia of ferns which aids in spore dispersal.
Term
Anther
Definition
Part of the stamen. A two-lobed structure of the filament. Contains pollen sacs.
Term
Antheridia
Definition
The male gametangia of bryophytes and ferns. It consists of a sterile jacket layer surrounding the spermatogenous cells on a stalk, which produce sperm cells. Sperm must swim through water to reach the archegonia with the egg.
Term
Antheriophores
Definition
The disk-shaped, flat-topped gametophores which hold up the antheridia of Marchantia.
Term
Anthoceros
Definition
The most familiar genera of Anthocerotophyta. Some are unisexual, some bisexual. In bisexuals, antheridia development comes before archegonia development. The sporophyte is an upright, elongated structure that lacks a seta. The foot is embedded in the gametophyte. There is a meristem at the base which elongates the sporophyte for a long period, so that all stages of spore development can be seen in a single sporophyte. The sporophyte is photosynthetic and green, covered with a cuticle, and has stomata that remain permanently open. Between spores, pseudoelaters twist as the sporophyte dies, dehiscing spores.
Term
Anthocerotophyta
Definition

Hornworts

Bryophytes. Some are thalloid. More than 300 species. They have horn-shaped sporophytes. The gametophytes resemble thalloid liverworts. Cells have a single large chloroplast with a pyrenoid or many chloroplasts and no pyrenoid. The gametophyte is rosette-shaped with dichotomous branching, usually 1 - 2 cm across, without conspicuous internal differentiation. There are large cavities containing colonies of Nostoc, embedded in mucilage, where they fix nitrogen for the hornwort. Pores on the lower epidermis are entry sites for Nostoc. Many cells secrete mucilage for water retention. Some hornworts have associations with glomeromycetes. Most hornworts are unisexual. Gametangia are on the dorsal surface of the gametophyte, with antheridia clustered in chambers. Many sporophytes may form from the same gametophyte. Includes Anthoceros.

Term
Anthocyanins
Definition
Flavonoids including pelargonidin, cyaniding, and delphinidin. Water soluble. Found in vacuoles. The pH of the cell affects what colour shows. Plants may change colour after pollination.
Term
Anticlinal division
Definition
Cell plats form perpendicular to the surface of the meristem. Occurs in the tunica layer of the shoot apical meristem.
Term
Antipodals
Definition
Three cells in the embryo sac at the chalazal end. Degrade after fertilization; have no function.
Term
Antirrhinum majus
Definition

Snapdragons

A model organism for studying homeotic genes.

Term
Apical-basal pattern
Definition
A body pattern established in embryogenesis. Pattern along the main axis.
Term
Apical cell
Definition
A cell in proembryo state. Towards the chalazal end. Gives rise to most of the mature embryo.
Term
Apical dominance
Definition
Achieved through redistribution of auxin, a plant hormone that inhibits auxillary bud elongation. Cutting the op off a plant will cause loss of apical dominance, leading to excessive branching.
Term
Apical meristem
Definition
Meristems at the tips of all roots and shoots. Produces primary growth. Indeterminate. Includes the root and shoot apical meristems, both of which contain all three primary mersitems.
Term
Apical placentation
Definition
A single ovule occurs at the apex.
Term
Apoplastic pathway
Definition
Moving through the protoplast or through cell walls.
Term
Arabidopsis thaliana
Definition
A model organism for studying homeotic genes. Has 4 green sepals, 4 white petals, 6 stamens (two shorter than the other four), and 1 pistil composed of two fused carpels. There are two locules in the ovary, and numerous ovules. Flower development is controlled by the ABCDE model.
Term
Archaea
Definition

"Ancient ones"

A domain of life. Thrive in extremely hot or acidic environments which are hostile to other organisms.

Term
Archaefructus
Definition
The oldest angiosperm in the fossil record. Dated to early Cretaceous period, 125 million years ago. Discovered in northern China. A small, herbaceous aquatic plant with nonshowy flowers, lacking a perianth.
Term
Archegonia
Definition
The female gametangia of bryophytes and ferns. Consists of a venter surrounding an egg on a stalk, and a neck lined with neck canal cells. After fertilization the zygote remains in the archegonia. After fertilization the zygote remains int eh archegonia, which supplies it with matrotrophy as it develops into a sporophyte. There are no plasmodesmata between gametophyte and sporophyte. Nutrient exchange is faciliated by the placenta.
Term
Archegoniophore
Definition
The umbrella-shaped gemetophore which holds up the archegonia of Marchantia.
Term
Artificial systems
Definition
Systems of classification based on one or a few characteristics.
Term
Asexual reproduction
Definition

Vegetative reproduction

Produces progeny that are genetically identical to the single parent. Meiosis and fertilization are absent. There is a wide variety of means of asexual reproduction. Many plants produce both sexually and asexually. Plants who reproduce only asexually had sexually reproducing ancestors. Requires less energy than sexual reproduction. Provides means to reproduce in the absence of mating. Allows for exact replications of individual well-suited to a certain environment. Populations cannot adjust to changing conditions as rapidly as sexually reproducing species. Mutations are always passed on to offspring. If a new disease arises, the entire population can be affected.

Term
Asteraceae
Definition

Composites

Eudicots. One of the most specialized and numerous families of flowers. Each flower has two fused carpels with a single ovule in one locule. Five stamens, fused to one another and to the corolla. Five petals are fused to one another and to the inferior ovary. Sepals are absent or reduced to bristles/scales, and may have a pappus. Each composite flower consists of disk flowers in the centre and ray flowers in the periphery. The composite head appears to be one flower. Each true flower matures at a different time, increasing genetic diversity; many pollination events occur.

Term
Asymmetric division
Definition
The first cell division in embryogenesis. Produces the apical and basal cell of the proembryo. Establishes apical-basal pattern and polarity.
Term
atpB
Definition
The gene that encodes for a subunit in ATP synthase. Useful in studying relationships between plants.
Term
Austrobaileyales
Definition
A basal grade angiosperm. Shrubs adapted to low light intensity.
Term
Autotroph
Definition

"Self feeder"

Satisfy energy requirements by producing their own complex organic compounds (including carbohydrates, fats, and proteins) from simple inorganic molecules. Typically use energy from sunlight to produce organic compounds using photosynthesis. Provide complex organic compounds for all heterotrophs.

Term
Auxin-based model
Definition
An explanation for phyllotaxis. Primordium initiation is directed by PIN1 auxin efflux carrier. High concentrations of auxin are required for initiation of a new leaf primordium. Auxin is depleted from surrounding cells, preventing initiation of additional primordia in the vicinity. Auxin acts on cell walls, leading to rapid growth.
Term
Axial system
Definition
Xylem and phloem. Produced by fusiform intials in the vascular cambium.
Term
Axil
Definition
The upper angle formed between the stem and petiole or leaf blade.
Term
Axile placentation
Definition
Ovules are borne on a central column of tissue that is partitioned into locules.
Term
Axillary bud
Definition
A component of a phytomere. Develop from bud primordia. Dormant until sufficiently distant from the shoot apical meristem. Can remain dominant for a long time.
Term
Axillary meristem
Definition
A detached part of the primary shoot meristem. Forms axillary buds.
Term
Axis
Definition
The "backbone" of the plant. Established with the asymmetric division of embryogenesis.
Term
Bacteria
Definition
A domain of life.
Term
Bark
Definition
Vascular cambium, secondary phloem, periderm, and any dead epidermis remaining outside of the periderm. The appearance of bark depends on how the periderm is formed. Includes outer bark and inner bark.
Term
Basal body
Definition
A structure in the cytoplasm from which flagella or cilia grow. Resembles a flagellum in structure, except the outer tubules are in triplets rather than in pairs, and the two central tubules are absent.
Term
Basal cell
Definition
A cell in the proembryo. Towards the micropylar end. Produces the suspensor.
Term
Basal grade angiosperm
Definition
Sister groups to all other flowering plants. Includes Amorellaceae, Nymphaeales, and Austrobaileyales.
Term
Basal placentation
Definition
A single ovule occurs at the base.
Term
Bats
Definition
A pollinator, especially in tropical flowers. Flowers produce copious nectar, and are a dull colour. Many open only at night.
Term
Beauty
Definition
A use for plants. Plants can be used as national emblems, for recreation or decoration, and can have historical, cultiral, religious, and/or mythological significance. Example: poppies, tulips, maples, spices.
Term
Bee
Definition
The most important pollinator. Visit the most number of plant species. Adult bees live on nectar and collect pollen to feed to larvae. Can see in ultraviolet, and cannot see red. Flowers pollinated by bees are showy, brightly coloured (usually blue or yellow), with distinctive patterns including "honey guides" that guide them to nectar.
Term
Bee's purple
Definition
Ultraviolet mixed with yellow. A common colour in bee pollinated flowers. Appears yellow to our eyes.
Term
Beetles
Definition
A pollinator. Attracted by floral odors. Essential floral parts are covered to prevent predation.
Term
Beltsville group
Definition
A USDA team in Beltsville, Maryland that studied photoperiodism in lettuce seeds.
Term
Benzaldahyde
Definition
A secondary metabolite produced by white campions. Produces the smell of almonds, which attracts moths.
Term
Berry
Definition
A fleshy simple fruit. One or many seeds; all parts are fleshy/pulpy, except for the exocarp, which is skin-like or a thick rind. Example: tomatoes, grapes, dates, citrus, cucumber.
Term
Betacyanins
Definition

Betalains

Pigments in flowers composed of complex aromatic compounds that produce reddish pigment. Occurs in plants which cannot produce anthocyanins. Example: peets, Bougainvillea.

Term
Biennial
Definition
Annuals with a life cycle that covers two growing seasons. In the northern hemisphere, it crosses one calendary year. In the southern hemisphere, it is interrupted by winter. Seldom woody, but stems and roots may undergo secondary growth. Includes winter annuals.
Term
Big Bang Theory
Definition
The first organic molecules were probably formed by hydrothermal vents, lightning, rain and/or solar energy. They accumulated in the oceans and formed groups of aggregates, these groups then formed the first, most primitive cells. These then evolved and became more complex. They gained the ability to grow, reproduce, and pass on characteristics to subsequent generations. All living organisms today use identical genetic code (DNA) to create life. This is evidence that life on Earth emerged only once, and all living things share a common ancestor.
Term
Bilaterally symmetrical flowers
Definition

Irregular flowers

Zygomorphic: "yolk", "pair"

One or more members of at least one whorl are different from other members of that same whorl. Some have irregular colour patterns. Example: snapdragons, garden peas.

Term
Biome
Definition
Natural communities of wide extent, characterized by distinctive, climatically controlled groups of organisms.
Term
Biophysical forces
Definition
An explanation for phyllotaxis. A leaf primordium is initiated when a portion of the tunica surface bulges or buckles, brought on by localized reduction in the layer's ability to resist pressure from tissues below.
Term
Binomial system
Definition

"Two-term"

A system for naming species. The first term is the genus, and the second term is the specific epithet.

Term
Biosphere
Definition
The living world and its environment.
Term
Birds
Definition
A pollinator. Flowers have copious, thin nectaries and little odor. Flowers are often red or yellow.
Term
Bisexual gametophyte
Definition
Bears both sperm-producing antheridia and egg-producing archegonia. Homosporous.
Term
Bivalents
Definition
Pairs of homologous chromosomes paired together in synapsis during prophase I.
Term
Blade
Definition

Lamina

The exposed portion of a leaf.

Term
Border cells
Definition
A component of the root cap. Cells on the periphery of the root cap. Secrete mucilage. They are sloughed off and separate from the root cap as they approach the periphery of the root cap. They may stay alive in the soil for several weeks. They have a change in gene expression and sequester carbon into the soil. 10 - 10,000 border cells are sloughed a day. They create a mucilage sheath and protect the root apical meristem from infection, maintain root-soil contact, mobilize essential elements, protect the root from deisccation, attract or repel bacteria, and decrease friction of the soil as the root grows.
Term
Bordered pit
Definition
A pit where the secondary wall arches over the pit, forming a pit cavity.
Term
Boscia albitrunca
Definition

Shepherd's tree

The plant with the deepest roots: 68 m deep. Lives in teh Kalahari Desert.

Term
Bract
Definition
A modified leaf associated with a stem, flower, or inflorescence.
Term
Branch traces
Definition
Connect axillary buds to the vascular system. There are usually two branch traces per bud.
Term
Branching
Definition
A step in the evolution of vascular plants. Branching of apical meristems, increasing surface area for photosynthetic capacity.
Term
Bryidae
Definition

True moss

A class of moss; most moss species. The protonema has branching filaments with single rows of cells. Leafy gametophytes develop from budlike structures on the protonema. In some species the protonema is the dominant form. The gametophyte can be up to 50 cm in length. Has mutlicellular rhizoids, leaves one cell thick (except at the midrib). Some species have hadrom and leptom.

Gametangia are on the tip of the main axis or on a lateral branch. Some genera are unisexual, some bisexual. Several antheridia are often on a single leafy structure called the splash cup.Insects may carry sperm-laden water from plant to plant.

Sporophytes take 6 - 18 months to mature, and are elevated on seta which can be up to 20 cm long, and can have hadrom and leptom. Some are brightly coloured to attract insects. Stomata are present on the sporophyte; some species have just one doughnut-shaped guard cell. The young sporophyte is photosynthetic, but when it matures it becomes yellow, orange, then brown. When mature the calyptra and operculum burst off, revealing the peristome and dispersing spores.

Reproduces aseuxally by fragmentation or with specialized features.

Many species are endemic to an area, and have species which live, breed, and feed off of it. Loss of Bryidae species could be catastrophic.

There are cushiony and feathery mosses.

Term
Bryphyta
Definition

Mosses

Bryophytes

Many non-moss species are called "moss". Mosses have five classes: Sphagnidae, Andreaeidae, Bryidae.

Term
Bryophytes
Definition

Nonvascular plants

A paraphyletic group including Bryophyta, Marchantiophyta, and Anthocerotophyta. Small, leafy, or flat plants. Cells are not lignified, and are connecte dby plasmodesmata. Have disk-shaped plastids. Limited to growing in moist locations because they lack vascular tissues. Often found in temperate or tropical forests, or along the edge of wetlands or streams, however they are not confined to such habitats.

The gametophytes are larger than the sporophytes, and free-living. Bryophytes have pores and rhizoids. Marhcntiophyta and Anthocerotophyta are thalloid.

Sporophytes are smaller and permanently attached to, and dependent on, the parental gametophyte.

Many bryophytes can reproduce asexually by fragmentation.

Reproduce sexually by gametic meiosis. Gametes are produced by antheridia and archegonia. Some species are unisexual and some are bisexual.

Significant in the ecosystem and carbon cycle, and important initial colonizers of bare rock and soil substrates.

Term
Bud primordia
Definition
Develop into axillary buds.
Term
Bulb
Definition
A large bud with small, conical stems with numerous modified scale-like leaves with thickened bases where food is stored. Roots arise form the bottom of the stem. Example: onion.
Term
Bulliform cells
Definition

Motor cells

Occur in longitudinal rows in the epidermis of some grasses. Participate in the mechanism of folding and unfolding of leaves in response to changes in water potential. Become flaccid with water loss, folding the leaf.

Term
Bundle sheath
Definition
One or more layers of compactly arranged cells with Casparian strips that ensure no part of the minor veins is exposed to air. Analogous to the endodermis of the root. Connected to the epidermis by bundle-sheath extensions. May have Kranz anatomy.
Term
Bundle-sheath extensions
Definition
Connect to the bundle sheath to the upper and/or lower epidermis. In some plants they conduct water to the epidermis.
Term
Burls
Definition

Lignotubers

Woody outgrowths at the base of the stems of shrubs and small trees in the Mediterranean type of climate of the Californian chaparrals. Contain dormant buds that sprout after the shoots are mechanically damaged or burned.

Term
Butterflies and diurnal moths
Definition
Pollinators. Attracted by nectar. Flowers often have "landing platforms".
Term
C3 grasses
Definition
The mesophyll cells are not radially arranged around hte bundle sheath: veins are surrounded by two bundle sheaths including a mestome.
Term
C4 grasses
Definition
There is Kranz anatomy around the bundle sheaths.
Term
Callase
Definition
Digests the callose cell walls of pollen grains in the pollen sacs so that they break apart. Secreted by the tapetum.
Term
Callose
Definition
A component of the cell wall. Spirally wound chains of glucose residues. Associates with sieve elements in the phloem. Formed in the cell walls of microsporocytes. Digested by callase. Deposited by the pollen tube as it grows to prevent breakange, allowing it to grow a long distance. Deposited in response to mechanical stress; seals plasmodesmata of damaged sieve elements. Includes wound callose and definitive callose.
Term
Calyptra
Definition
Develops from the venter in archegonia after fertilization. Partially or entirely covers the capsule.
Term
Calyx
Definition
The sepals of a flower. Part of the perianth.
Term
Cambial zone
Definition
The vascular cambium, including its initials and immediate derivatives. An indistinct layer.
Term
Campylopus
Definition
A bryophyte that grows on bare areas of volcanoes in Antarctica, where temperatures may reach 30ºC.
Term
Capsule (bryophtyes)
Definition
A component of the sporophyte in bryophytes. Contains the sporangium; surrounded by the calyptra. Attached by the seta to the foot.
Term
Capsule (fruit)
Definition
A dehiscent, dry simple fruit. Derived from a compound ovary (more than one carpel). Release seeds in a variety of ways: may open longitudinally, or through openings at the top. Example: poppy.
Term
Carboniferous Period
Definition

"I carry coal"

300 - 400 million years ago

There was huge climate change. Lepidodendron dominated hot, humid swamps, and contributed to development of coal deposits. CO2 levels in the atmosphere decreased due to Lepidodendron. Humidity decreased, and swamps dried up, killing Lepidodendron and beginning the Ice Age.

Term
Carl Linneas
Definition

1701 - 1778

In 1783, he published Specis Planatarum. Created the binomial system.

Term
Carotenoids
Definition
Pigments that produce red, orange, yellow, and ultraviolet colours. Oils soluble, found in chloroplasts and chromoplasts.
Term
Carpel
Definition
A reproductive flower part: bears ovules, which develop into seeds after fertilization. Develops into the fruit wall after fertilization. Collectively, they form the gynoecium. Includes the ovary, style, and stigma. May be fused into a pistil. For carpel development in the ABCDE model, class C and E function is needed.
Term
Carpelate
Definition

Pistillate

Imperfect flowers with carpels.

Term
Caryopsis
Definition

Grain

An indehiscent, dry simple fruit. The seed coat is fused to the pericarp over its entire surface.

Term
Casparian strips
Definition
Wall thickenings in the cells of the endodermis, and in bundle sheaths. Attached to the primary cell wall, middle lamella, and plasma membrane. Impregnated with suberin and sometimes lignin. Creates a hydrophobic barrier that enforces symplastic movement of water and minerals into the vascular bundle of the root. Prevents air contact with the vascular bundle of the leaf.
Term
Castor bean
Definition
A eudicot with epigeous germination. Food is stored in the endosperm of the seed, and absorbed by cotyledons as they emerge.
Term
Category
Definition
The level at which a taxon is arranged. The categories are: kingdom, phylum, class, order, family, genus, and species.
Term
Caulerpa taxifolia
Definition
A member of Codium. Released accidentally from the Oceanographic Museum of Monaco in 1984, and now it is a serious invasive species that expands an average of 50 km each year.
Term
Cell cycle
Definition
Divided into two phases: interphase and cell division. Progression is mediated by checkpoints.
Term
Cell division
Definition

M phase

The second phase of cell cycle. Cells reproduce. The contents of a cell are divided between two daughter cells. The means by which single-celled organisms reproduce, and by which multi-cellular organisms grow and replace injured or worn out tissues. Has two phases: mitosis and cytokinesis.

Term
Cell plate
Definition
The initial partition between daughter cells that forms in cytokinesis. Forms from fusing vacuoles of the Golgi apparatus. Plasmodesmata form. Initially consists mostly of callose. Contains hemicellulose and pectins. Forms between two phragmoplasts. Grows outwardly to fuse with the cell wall of the parent cell at the zone previously occupied by the preprophase band: guided by actin filaments. The middle lamella forms between the newly formed cell wall between cells.
Term
Cell sap
Definition
The contents of the tonoplast. Water, inorganic ions, sugars, organic acids, amino acids. Composition varies with species, cell type, and development. Sometimes the contents can crystalize in high concentrations (calcium oxalate).
Term
Cell wall
Definition
A stiff outer wall on cells. In the endosymbiotic theory prokaryotes lost their cell wall and became primitive phagocytes. Constrains the expansion of the protoplast, preventing rupture of the plasma membarne. Plant cell types are identified by the structure of their cell walls. Absorbs, transports, secretes, defense, information reception. Contains polysaccharides and oligasaccharins: cellulose, hemicellulose, pectin, callose, glycoproteis, lignin, cutin, suberin, and waxes. Loosened by expansins and some hormones. Includes the middle lamella, primary wall, and secondary wall.
Term
Cellular organization
Definition
An attribute of living things.
Term
Cellular-type
Definition
A type of endosperm development. Divisions in the endosperm are always followed by cytokinesis. There is no free-nuclear stage.
Term
Cellulose
Definition
The principle component of the cell wall. Bundled into microfibrils, secreted by cellulose synthase, which wind together to form micelles which are arranged in macrofibrils that form the cell wall. Laid down perpendicularly to the axis of elongation of hte cell, or if the cell is expanding outwardly, in a random pattern. Microfibrils run parallel to cortical microtubules just below the plasma membrane.
Term
Cellulose synthase
Definition
Rosette-shaped complexes of six subunits in the plasma membrane. Synthesizes microfibrils.
Term
Central cell
Definition
A binucleate cell in the centre of the embryo sac. Contains the polar nuclei.
Term
Central zone
Definition
A region of the shoot apical meristem. The corpus layer and overlying tunica layers. Cell divisions are relatively infrequent. Analogous to the quiescent centre of the root apical meristem.
Term
Centriole
Definition
Structure present in some cells, identical to the basal bodies of flagella. Surrounded by the centrosome. Duplicated in G1 phase.
Term
Centromere
Definition
Where sister chromatids connect to form the chromosome. DNA sequences tha tbind to the mitotic spindle in metaphase. There is a kinetochore on either side of the centromere.
Term
Centrosome
Definition
A cloud of amorphous material that surrounds the centriole. Duplicated in G1 phase.
Term
Chalazal end
Definition
The end of the embryo sac opposite from the micropyle. The three antipodal cells are at this end.
Term
Chara
Definition

Stonewort

A group within Charales. Has calcified cell walls. Sperm are produced by antheridia. Eggs stay enclosed in oogonia. The sperm are the only flagellated cells in their life cycle. Zygotes are encased in sporopollenin.

Term
Charales
Definition
A group of desmids. 81 - 400 living species. Green algae, primarily fresh water, sometimes in brackish water. Includes Chara.
Term
Charles Darwin
Definition

Wrote On the Origin of the Species

"Probably all of the organic beings that ever lived on this earth have descended from some one primordial form, into which life was first breathed."

Term
Charophyceae
Definition

Charophyte algae

Streptophyte algae

Charophytes

Unicellular, colonial, filamentous, and parenchymatous genera. Have similarities to bryophytes and vascular plants. All have zygotic meiosis. Divergent members include Mesostigma, Chlorokybus, Klebsormidium, and Spirogyra.

Term
Checkpoints
Definition
Points in the cell cycle which can only be passed if there is successful activation of kinases. There is one at the end of G1, at the end of G2, and during anaphase
Term
Chemoattractants
Definition
Chemicals that attract sperm cells. Released by synergids.
Term
Chiasma
Definition

Plural, chiasmata

The point in the synaptonemal complex of homologous chromosomes where crossing-over occurs during prophase I. It makes an X-shpaed configuration. At least one chiasma appears.

Term
Chlamydomonoas
Definition
A chlorophyte with zygotic meiosis. Unicellular, motile, Has two equal flagella. A model for studies on genes regulating photosynthesis. Has a red chloroplast, can reproduce asexually and sexually, with isomorphic zygotic meiosis. Gametes are zoospores. During fertilization there is plasmogamy then karyogamy. The zygote undergoes a period of dormancy before undergoing meiosis to form four haploid individuals.
Term
Chlamydomonoas
Definition
A chlorophyte with zygotic meiosis. Unicellular, motile, Has two equal flagella. A model for studies on genes regulating photosynthesis. Has a red chloroplast, can reproduce asexually and sexually, with isomorphic zygotic meiosis. Gametes are zoospores. During fertilization there is plasmogamy then karyogamy. The zygote undergoes a period of dormancy before undergoing meiosis to form four haploid individuals.
Term
Chlorenchyma
Definition
Parenchyma cells with chloroplasts. Includes mesophyll.
Term
Chlorcoccum
Definition
A unicellular, non-motile chlorophyte. Found in soils. Reproduces asexually by producing biflagellated zoospores. Reproduces sexually by releasing gametes that fuse to form zygotes, which have zygotic meiosis.
Term
Chlorokybus
Definition
A rare terrestrial and freshwater green algae charophyte. Packets of cells are held together in mucilage.
Term
Chlorophyceae
Definition

Chlorophytes

A class of algae. Flagellated and non-flagellated, unicellular and multi-cellular, motile, non-motile, colonial, filamentous, and in flat sheets. Mainly live in freshwater, but there are some marine species. Includes snow algae. Have zygotic meiosis. Includes Chlamydomonas, Volvox, Chlorococcum, Hydrodictyon, Oedogonium, and Fritschiella.

Term
Chlorophyll
Definition
Green pigment found in chloroplasts. Fat soluble.
Term
Chlorophyte clade
Definition
Contains most green algae.
Term
Chloroplasts
Definition
A plastid. The site of photosynthesis. Contains chlorophyll and carotenoid pigments in the thylakoid membrane. Found in plants and green algae. In plants they are disk shaped, 4 - 6 μm in diameter, and arrange themselves in the cell to optimize light exposure. The thylakoids form grana, which are connected by stroma thylakoids. Have a nucleoid with its own DNA, but has no histones, and receives most of its proteins and fuel from the cytoplasm. Synthesizes some amino acids, fatty acids, and secondary metabolites. Evolved from cyanobacteria or green algae endosymbiont.
Term
Choleochaetales
Definition
About 20 species of desmids, including branched filamentous, and discoid genera. Includes Choleochaete.
Term
Choleochaete
Definition
A group within Choleochaetales. Grows on the surface of submerged rocks or freshwater plants. Uninucleate, vegetative cells, each with one large chloroplast. Very similar to chloroplasts and pyrenoids that occur in hornworts. Reproduces asexually by zoospores formed within cells. Sexual reproducition is oogamous: zygotes remain attached to the parental thallus, where they are covered by a layer of transfer cells which provide nutriensts.
Term
Chromatin
Definition
Can be seen if the cell is stained. DNA combined with histone proteins. During nuclear division it becomes condensed into chromosomes.
Term
Chromoplast
Definition

"Colour"

A plastid. Pigmented plastids. Lack chlorophyll, but synthesize and retain carotenoid pigments. Found in flowers, aging leaves, fruits, and roots. May develop from chloroplasts when chlorophyll disappears, such as in the ripening of fruits. Helps the plant attract animals with which the plant has co-evolved (for pollination or seed dispersal).

Term
Chromosomes
Definition
Condensed units of chromatids. Species differe in the number of chromosomes. Consists of two identical sister chromaitds connected at the centromere.
Term
Cilia
Definition

Singular, cilium

Short, hair-like structures in great numbers on the surface of some cells. Have movement similar in mechanism to that of a flagellum. Grow from basal bodies in the cytoplasm.

Term
Cis face
Definition
The forming side of the Golgi body. Faces towards the ER.
Term
Cisternae
Definition

Singular, cisterna

Flattened sacs of membrane in the rough ER, or in the Golgi bodies. In the Golgi body, subsequent steps in synthesis occur in each cisterna.

Term
Cladistics
Definition
The most widely used method of classifying organisms. A form of phlyogenetic analysis, seeking to understand phlogenetic relationships. Recognizes monophyletic groups by their synaptomorophies.
Term
Cladogram
Definition
A graphical representation of a hypothesis of phylogenetic relationships among a group of organisms. Constructed using the principle of parsiomony.
Term
Cladophora
Definition
A genera of Ulvophyceae. Filamentous, multinucleate sepate cells. Can form blooms in freshwater. Either free-floating or attached to rocks and vegetation. Have isomorphic, sporic meiosis.
Term
Cladophyll
Definition
Stems that assume the form and closely resemble leaves. True leaves have axillary buds; cladophylls do not. Example: feathery branches of asparagus (the scales on the spears are true leaves).
Term
Class
Definition
The category below phylum and above order.
Term
Class A
Definition
Genes in the ABC model that affect whorls 1 and 2: sepals and petals. Encoded by AP1 and AP2. Mutually antagonistic with class C genes: deletion of one causes proliferation of the other. Loss of class A gene function results in formation of carpels instead of sepals in the first whorl, and stamens instead of petals in the second whorl.
Term
Class B
Definition
Genes in the ABC model that affect whorls 2 and 3: petals and stamens. Encoded by AP3 and PI. Loss of class B gene function results in formation of sepals instead of petals, and carpels instead of stamens.
Term
Class C
Definition
Genes in the ABC model that affect whorls 3 and 4: stamens and pistils. Activated by AG. Mutually antagonistic with glass A genes: deletion of one causes proliferation of the other. Loss of class C genes results in formation of sepals instead of petals, and carpels instead of stamens.
Term
Class D
Definition
Genes in the ABCDE model. Discovered in petunias. Needed for ovule development and seed dispersal. Encoded by STK.
Term
Class E
Definition
Discovered in tomatoes and petunias. Genes in the ABCDE model. Class A, B, and C genes need class E genes to be functional in order to produce floral orangs. Encoded by SEP. A mutation in SEP 1 - 3 produces sepals in all whorls. A mutation in SEP4 results in leafy mutation.
Term
Clathrin
Definition
A protein that coats coated vesicles, and forms a cage around the vesicle.
Term
Clonal regeneration
Definition
A function of roots. Can produce buds that develop into new shoots.
Term
Closed meristem
Definition
The root cap and root body are clearly distinct, having originated form dedicated initials.
Term
Closed type
Definition
A type of apical organization of roots. Each region in the final root has its own initials.
Term
Closed vascular bundles
Definition
Usually entirely surrounded by a sheath of sclerenchyma cells.
Term
Club mosses
Definition

Lycopodiophyta

A member of lycophytes.

Term
CLV
Definition

CLAVATA

The gene that regulates meristem size by repressing initial cell activity. Loss of CLV genes causes accumulation of undifferentiated cells in the central zone, increasing the size of the meristem. Includes CLV1, CLV2, and CLV3.

Term
Coat-imposed dormancy
Definition
Dormancy where the seed coat is impermeable to water and oxygen. The seed coat prevents the radicle from exiting, and releasing growth inhibitors that suppress growth of the embryo. Conifers, cereals, and some eudicots have coat-imposed dormancy.
Term
Coated vesicles
Definition
Packages newly formed proteins from the Golgi bodies. Coated in clathrin proteins.
Term
Codium
Definition
A group of siphonous marine algae. A spongy mass of densely intertwined filaments. Includes Codium fragile, Caulerpa taxifolia, Ventricaria, Acetabularia, and Halimeda.
Term
Codium fragile
Definition
A member of Codium. Weedy nuisance growths that spread in waters of temperate zones.
Term
Coleoptile
Definition
A structure that covered the plumule of grass embryos.
Term
Coleorhiza
Definition
A structure that covers the radicle in grass embryos.
Term
Collenchyma cells
Definition
The constituents of collenchyma tissues.
Term
Collenchyma tissue
Definition
A ground tissue. Live at maturity. Consists of collenchyma cells. Occurs in discrete strands, or as continous cylinders beneath the epidermis in stems and petioles, and in the borders of veins in eudicot leaves. The "strings" in celery stalks. Unevenly thickened, non-ligified primary walls, often soft and pliable with a glistening appearance in fresh tissue. Develop thick, flexible walls which the organ elongates. Adapted for support of young, growing shoot organs, or in plants that lack secondary growth. Roots rarely have collenchyma. May be absent in the stems of plants that develop sclerenchyma early in development. It has angualr, lamellar, or lacunar organization.
Term
Columella
Definition
A component of the root cap. The central column of cells.
Term
Column
Definition
The fused stamens and carpel of Orchidaceae flowers.
Term
Companion cell
Definition

Sib cell

A parenchyma cell that contains all cell components including the nucleus. Closely associates with a sieve tube element with numerous plasmodesmata. Deliver substances to the sieve tube element to keep it alive: information molecules, proteins, ATP.

Term
Competency
Definition
The ability of a cell to develop in response to specific signals.
Term
Complete flowers
Definition
Flowers that include all four floral organs: sepals, petals, stamens, carpels.
Term
Complex thalloid liverworts
Definition
A type of liverwort. Has internal tissue differentiation. The thallus is 20 cells thick at the midrib. Includes Riccia, Ricciocarpus, and Marchantia.
Term
Complex tissues
Definition
Tissues composed of more than one type of cell. Includes vascular and dermal tissues.
Term
Compound leaf
Definition
A leaf divided into several distinct leaflets, each with a small petiole (petiolule). Either pinnate or plamate.
Term
Compound middle lamella
Definition
The combined primary cell wall and middle lamella, when it is difficult to distinguish between the two, especially where secondary walls are thick.
Term
Compression wood
Definition
Reaction wood found in conifers. Develops on the underside of the leaning part. Higher in lignin and lower in cellulose than most woods.
Term
Conducting phloem
Definition
Phloem which is living and functional. In the inner bark.
Term
Conduction
Definition
A function of roots.
Term
Coniferophyta
Definition
A phyla within Plantae. Seed-producing vascular gymnosperms. Contains conifers.
Term
Connation
Definition
When floral parts are united with other members of the same whorl.
Term
Convergent evolution
Definition
Similar conditions leading to the evolution of similar adaptations in different species. Leads to analogous structures.
Term
Cork
Definition

Phellem

A tissue of the periderm. Non-living at maturity. Dead at maturity, and walls are heavily suberized. Arises from the outer surface of the cork cambium. Highly impermeable to water and gasses.

Term
Cork cambium
Definition

Phellogen

A tissue of the periderm. A lateral meristem. Forms cork on the outer surface, and phelloderm on the inner surface. Origin is variable.

Term
Corm
Definition
Similar to a bulb, but consists mostly of thickened, fleshy stem tissue. Leaves are commonly thin and much smaller. Example: gladiolus.
Term
Corolla
Definition
The petals of a flower. Part of the perianth.
Term
Corpus
Definition
A component of the tunica-corpus organization of the shoot apical meristem. Beneath the tunica layers. Cells divide periclinally. Adds bulk to the developing shoot. There is one layer of corpus initials.
Term
Cortex
Definition
Occupies the greatest volume of primary body of most roots. Bound by the epidermis, and encloses the vascular cylinder. The outer cortex has collenchyma, and the inner cortex has parenchyma. Plastids in the cortex store starch, and usually lack chlorophyll.
Term
Cotical cytoplasm
Definition
Cytoplasm near the periphery of the cell. Contains the cortical ER.
Term
Cortical ER
Definition
Endoplasmic reticulum in the cortical cytoplasm. Regulates levels of ions in the cytosol, playing a role in developmental and physiological processes involving Ca, and in structural stability of the cytoskeleton, and in intercellular transport through plasmodesmata. An indicator of metabolic and developmental status of a cell. Quiescent cells have less cortical ER.
Term
Cotton
Definition
A major fibre crop. Used to make US dollar bills.
Term
Cotyledon
Definition
The seed leaf. Monocots have one. Eudicots have two. In some species the cotyledons absorb nutrients form the endosperm and/or perisperm before maturation, and act as the embryo's main nutrient source; the cotyledons are large and fleshy. In some species the endosperm is the main food source fo the embryo, and cotyledons are thin and membranous. In monocots the cotyledon absorbs nutrients from the cotyledon. The cotyledon of grasses is the scutellum.
Term
Cox1
Definition

CO1

Genes that encode for cytochrome oxidase 1. Present in the mitochondria of all animals. Used as a universal DNA barcode for animals. Varies wildly between species, but rarely between individuals of one species. Not suitable as a barcode for plants.

Term
Cristae
Definition

Singular, crista

Folds or tubules in the inner membrane of a mitochondrion, which increase the surface area available to proteins. Encloses the matrix.

Term
Crossing over
Definition
During prophase I, chromatids break apart and rejoin with corresponding segments of their homologous chromosomes, in the synaptonemal complex. Usually at least one chiasma appears.
Term
Cushiony moss
Definition
A growth type of true moss. Gametophytes are erect and have few branches, usually with terminal sporophytes.
Term
Cuticle
Definition
A waxy layer in the epidermis that reduces water loss, but prevents gas exchange between plants and surrounding air.
Term
Cutin
Definition
A component of the cell wall. Found in the cell walls of the epidermis. Occurs in combination with waxes.
Term
Cycadophyta
Definition
A phyla within Plantae. Seed-producing vascular gymnosperms. Contains cycads.
Term
Cyaniding
Definition
An anthocyanin that produces violet colour.
Term
Cyanobacterium
Definition
A free-living, photosynthetic bacteria. Evolved into the chloroplasts of algae in the endosymbiont theory.
Term
Cypsela
Definition
An indehiscent, dry simple fruit. Characteristic to asteraceae. Similar to achenes, but derived from an inferior ovary.
Term
Cytokinesis
Definition
The second phase of cell division. The entire cell is divided into two daughter cells with a nucleus with full chromosome complement and approximately half of the cytoplasm. The cell plate appears.
Term
Cytoplasm
Definition
The contents of the protoplast inside the plasma membrane. Has cytoplasmic streaming. Includes the cytosol, plastids, mitochondria, endomembrane system, cytoskeleton, ribosomes, peroxisomes, vacuoles, the nucleus, and oil bodies.
Term
Cytoplasmic streaming
Definition

Cyclosis

The constant motion of the cytoplasm as long as the cell is alive. Facilitates transport of materials within the cell and into/out of its environment. Mediated by actin filaments.

Term
Cytoskeleton
Definition
A component of the cytoplasm. A dynamic network of protein filaments that extends throughout the cytosol, involved in many processes: cell division, growth, differentiation, movement of organelles. In plants the cytoskeleton consists of microtubules and actin filaments.
Term
Cytosol
Definition

Cytoplasmic matrix

A component of the cytoplasm. The cellular "soup": the fluid in which other cytoplasm contents float.

Term
Daughter cells
Definition
Two cells produced from cell division.
Term
Daughter chromosomes
Definition
Separated sister chromatids during anaphase.
Term
Dawsonia superba
Definition
The tallest true moss. The gametophtye is 50 cm tall.
Term
Day-neutral plants
Definition
Flower regardless of day length. Example: cucumber, sunflower, rice, maize, garden pea. Different geographic populatioins are precisely adjusted to the demands of the local daylight regimen.
Term
Decussate
Definition
A phyllotaxy. Each successive pair of leaves is at a right angle to the previous pair. Example: mint.
Term
Definitive callose
Definition
Callose deposited in the sieve areas of older sieve elements.
Term
Dehiscence
Definition
Opening of the pollen sacs. Pollination occurs.
Term
Dehiscent fruits
Definition
Dry simple fruits that split open at maturity. Commonly contain several seeds. Includes follicles, legumes, siliques, and capsules.
Term
Delphinidin
Definition
An anthocyanin that produces blue colour.
Term
Density
Definition
Weight per unit volume. Water has a density of 63.4 lbs/ft3, or 1 g/cm3.
Term
Derivative
Definition
A cell produced by division of an initial. It is not an initial, but it may divide several times before undergoing differentiation.
Term
Dermal tissue system
Definition
A fundamental tissue system. Originates from the protoderm. Surrounds the ground tissue system. Has complex tissues. There are two tissues: epidermis and periderm.
Term
Desiccation
Definition
A stage in seed maturation phase. The seed may lose up to 90% of its water content.
Term
Desmids
Definition
A large group of freshwater algae related to Spriogyra. Lack flagellated cells. Some are filamentous, some unicellular. Most have two parts connected at the isthmus. Similar reproduction to Spirogyra. Abundant in peat bogs and ponds poor in mineral nutrients. Some are associated with symbiotic bacteria that live in mucilaginous sheaths. Resemble bryophytes and vascular plants in sexual reproduction more closely than other charophytes; they share a common ancestor. Have to orders: Coleochaetals and Charales.
Term
Desmotubule
Definition
A modified tubule of the ER which passes through a plasmodesma.
Term
Determination
Definition
Progressive commitment to a specific course of development. Weakening or loss of capacity to resume growth. Cells differentiate at different times and with different strength.
Term
Development
Definition
The sum of total events that form an organisms' body. Occurs in response to genetic instructions, location of cells in tissues, and environmental factors. Three overlapping processes: growth, morphogenesis, and differentiation.
Term
Developmental plasticity
Definition
Growth is modified by the environment. The "behaviour" of plants.
Term
Differentiation
Definition
A step in the evolution of vascular plants. Development of different tissues: roots, stems, leaves, and stomata. Cells with identical genetic constitution become different from one another. Often begins while the cell is still growing. Determined by control of gene expression, and final position in the plant, determined by positional information exchange.
Term
Diffuse-porous woods
Definition
Woods where the early and late woods have similarly sized vessels.
Term
Dioecious
Definition

"Two houses"

When staminate and carpellate flowers are on different plants.

Term
Diploid (2n)
Definition

"Double set"

With two copies of genes.

Term
Disk flowers
Definition
Flowers in the centre of the composite head of Asteraceae flowers.
Term
Dispersal of spores
Definition
An adaptation that was necessary for vascular plants. Wind, insects, flowers.
Term
Distichous
Definition
A phyllotaxy. There is a single leaf at each node, and the leaves are disposed into opposite ranks. Example: grasses.
Term
Diversity in plants
Definition
Plants are diverse in structure, physiology, and reproductive strategies. This diversity reflects their adaptations to their environments.
Term
Domains
Definition
The largest grouping of life on Earth. There are three domains: Archaea, Bacteria, and Eukarya.
Term
Dominant allele
Definition
Expressed in homozygous individuals, and in heterozygous individuals, masking a recessive trait.
Term
Dormancy
Definition
The embryo has halted growth, and will not germinate, even if conditions become favourable. Caused by the seed coat and/or by the embryo. Includes primary and secondary dormancy. Ensures that the seed germinates in favourable conditions. Some seeds must pass through the digestive tracts of animals, be washed away by rainfall, mechanically cracked, or heated by fire in order to germinate. Includes photodormancy, stratification requirement, and after-ripening.
Term
Double fertilization
Definition
Found in angiosperms. Two sperm cells are deposited into synergid, which disintegrates. Actin and myosin move one sperm towards the egg and one sperm towards the polar nuclei. The sperm that fertilizes the egg forms the diploid zygote, and the sperm fertilizes the polar bodies (with triple fusion) forms the primary endosperm nucleus.
Term
Double flowers
Definition

A homeotic mutation that results in petals forming instead of stamens.

Example: garden roses. Wild-type roses have 5 petals, and the double flwoer mutation has 20 or more.

Term
Drupe
Definition

Stone fruit

A fleshy simple fruit. Generally has one seed. A thin, skin-like exocarp, fleshy mesocarp, and stony endocarp that encloses the seed.

Example: peach, cherry, olive, plum. A coconut is a drupe with a fibrous mesocarp.

Term
Dry stigma
Definition
A stigma where the cuticle contains a hydrated layer of proteins, carbohydrates, and lipids.
Term
Dynamic instability
Definition
A characteristic of microtubules. It is constantly being broken down and reformed.
Term
Early wood
Definition
Younger wood that is less dense, with wider cells and proportionally thinner walls.
Term
Ecosystem
Definition
An entity made from tansient individuals, some long-lived, some short-lived. Once in balance it does not change. Virtually every living thing is a food source for another living thing. Energy captured by plants goes through many organisms before being dissipated. Elements are continuously recycled. It is impossible to change a single component without risking destroying the balance. At the base of all ecosystems are plants, algae, and photosynthetic bacteria.
Term
Egg
Definition
The female gamete. In archegonia it is surrounded by the venter. In angiosperms it is found in the egg aparatus at the micropylar end.
Term
Egg apparatus
Definition
Three cells in the embryo sac: the egg, and two synergids. At the micropylar end.
Term
Elater
Definition
Curled structures that surround spores in the antheridia of Marchantia and Equisetopsida. Sensisitve to humidity, when the capsule dries, out, they untwist and disperse pollen.
Term
Elkinsia polymorpha
Definition
The oldest known vascular seed plant. Evolved 365 million years ago.
Term
Embryo
Definition
The young plant inside the seed. Includes the shoot apical meristem, plumule, epicotyl, cotyledon, hypocotyl, and radicle.
Term
Embryo-imposed dormancy
Definition
Dormancy controlled by the ratio of abscisic acid and gibberellic acid, and the physiological maturity of the embryo. Some embryos undergo after-ripening. The Roasaceae family, woody species, and some grasses have embryo-imposed dormancy.
Term
Embryo proper
Definition
THe second stage of embryogenesis. At first all cells are undifferentiated, then it develops spatially arranged primary meristems. Progresses into globular stage.
Term
Embryo sac
Definition
The megagametophyte in angiosperms. An eight-nucleate cell that becomes seven cells with eight nuclei: two polar nuclei (together from the central cell), the egg apparatus (one egg cell, two synergids), and three antipodals.
Term
Embryogenesis
Definition
The formation of the embryo. Accompanied by seed development. Continuous flow of nutrients from the female parent to the embryo. Establishes two body patterns: apical-basal and radial. Polarity and axis is established with the asymmetric division. Stages: proembryo, embryo proper, globular stage, heart stage, torpedo stage. Progresses into maturation phase.
Term
Embryophytes
Definition
All groups of land plants. Muticellular, matrotrophic embryos.
Term
Enations
Definition
The earliest forms of leaves. Clusters of photosynthetic stems.
Term
Endocarp
Definition
The inner layer of the pericarp.
Term
Endocytic vesicles
Definition
Vesicles containing engulfed particles as a result of endocytosis.
Term
Endocytosis
Definition
Uptake of extracellular substances by infolding of the plasma membrane to form a vesicle. May engulf large particles including other bacteria. Phagocytes are capable of endocytosis.
Term
Endodermis
Definition
The innermost layer of the cortex. Compactly arranged cells lacking air spaces, with Casparian strips. Includes passage cells.
Term
Endogenous
Definition

"Originating within"

Originating from deep within the parent root. Lateral roots are endogenous.

Term
Endomembrane system
Definition
A component of the cytoplasm. Includes ER, Golig appratus, vesicles, and various solutes. A continuous, interconnected system.
Term
Endoplasmic reticulum (ER)
Definition
A complex system of membranes that permeates the entire cytosol. Contains the lumen, and is continuous with the nuclear envelope. Plays a central role in cellular biosynthesis and membrane production. Produces vacuoles. Structure of the ER depends on cell type, metabolic activity, and development. Facilitates communication within the cell. Channels proteins and lipids to different parts of the cell. Has two continuous regions: rough ER and smooth ER. The anchor for everything in the cell.
Term
Endoreduplication
Definition

Endoreplication

Replication of DNA before differentiation. May occur more than once, resulting in large nuclei with multiple copies of each gene.

Term
Endosperm
Definition
Formed in the embyo sacs of angiosperms. Forms the primary endosperm nucleus, result of triple fusion of a sperm and the polar nuclei. A triploid body that acts as a nutrient source for the embryo. Often forms before the first zygotic division. Two types of development: nuclear-type and cellular-type.
Term
Endosymbiont
Definition
A cell living inside another cell. Mitochondria and chloroplasts both evolved from endosymbionts.
Term
Endosymbiotic Theory
Definition

Postulated in 1910 by Konstantin Mereschkowski. Explains the transformation of prokaryotic cells into eukaryotic cells.

Prokaryotes first lost the cell wall, becoming phagocytes. Sterols were incorporated into the plasma membrane, making it flexible. This allowed for the development of membrane-bound inner organelles and the nucleus. A cytoskeleton developed to provide support and aid in movement of hte cell and its internal components.

The phagocyte then enculfed smaller cells: alpha-proteobacterium and cyanobacteria, which lost unnecessary structures, transfered most of their DNA to the host, and became mitochondria and chloroplasts, respectively.

Evidence for this: mitochondria and chloroplasts have double membranes. The inner membrane originates from the original free-living bacteria, and the outer membrane originates from the plasma membrane of the host.

Term
Epicotyl
Definition
A stem-like axis with one or more young leaves above the cotyledons of the embryo.
Term
Epicuticular wax
Definition

Cuticle

A mixture of cutin and wax, deposited on the epidermis in smooth sheets or in a rod/filament style extending upwards.

Term
Epidermis
Definition
A dermal tissue. The outer protective layer of the primary plant body. Functionally diverse, compactly arranged cells, providing mechanical protection of the plant. Walls are covered with the cuticle that minimizes water loss. The wax can give the plants a "bloom" appearance. Light perception involved in circadian leaf movements and photoperiodism is sensed in the epdiermis. Cells include guard cells, subsidary cells, and trichomes.
Term
Epigeous germination (eudicot)
Definition
The hypocotyl elongates, forming the hook that pulls the shoot tip and cotyledons through the soil. Cotyledons photosynthesize, and wither when the seedling is established. Example: garden bean, castor bean.
Term
Epigeous germination (monocots)
Definition
The cotyledon elongates, forming the hook that pulls the seed upward. The plumule emerges from a protective sheath at the base of the cotyledon. Example: onion.
Term
Epigynous flower
Definition
The perianth and stamens rise from the top of the ovary. Example: apples.
Term
Epiphytes
Definition
Plants which grow on other plants, usually trees.
Term
Equisetopsida
Definition

Horsetails

A member of pterophytes. A phyla of seedless vascular plants that dominated from the Late Devonian period through the Carboniferous Period. Today there is only one genus: Equisetum. Have vegetative shoots, and reproductive shoots with cone-like strobili. Stems arise from rhizomes that bear wiry roots. Sporangia contract and split along the inner surface, elaters coil and uncoil, helping to disperse spores.

Term
Equisetum
Definition
The only living genera of Equisetopsida.
Term
Established
Definition
When the seedingl is no longer dependent on stored food of the seed: it is photosynthesizing.
Term
Ethyl methanesulfonate (EMS)
Definition
A mutagenic compound that creates random mutations. Reacts with guanine, forming abnormal pairs with thymine instead of cytosine. Used to produce homeotic mutants.
Term
Etiolated
Definition
When a plant grows in the dark, it has elongated stems, poor leaf development, and little to no synthesis of chlrophyll.
Term
Etioplast
Definition
A plastid. Forms when the protoplast is not exposed to light. Has prolamellar bodies. Develop into chloroplasts if exposed to light.
Term
Eudicots
Definition

Dicots

Dicotyledons

A classification of angiosperms. Flowers are in multiples of four or five. Triaperturate: has three pores or furrows on the pollen. Two cotyledons. Usually netted leaf venation. Vascular bundles in the stem are arranged in a ring, with pith. Secondary growth with vascular cambium is common.

Term
Eukarya
Definition

A domain of life. Contains eukaryotes. There are an estimated 10 million eukaryotic species. All organisms except bacteria and archaea are eukaryotes.

There are three kingdoms within Eukarya: Fungi, Animalia, and Plantae.

Term
Eukaryote
Definition
A cell belonging to Eukarya. Larger, highly structure, has a nuclear envelope, membrane-bound organelles, and complex chromosomes. According to fossil records, eukaryotes arose around the same time that oxygen in the atmosphere increased, 700 million years ago.
Term
Exine
Definition
The outer wall of a pollen grain. May be smooth or sculptured. Often scented, pigmented, and enzyme-rich. Often has pores or linear apertures: sites for pollen tube germination, and uptake of substances, giving the pollen grain the ability to contract and expand from osmotic pressures. Composed of sporopollenin.
Term
Exocarp
Definition
The outer layer of the pericarp.
Term
Exocytosis
Definition
A non-coated vesicel fuses with the plasma membrane to discharge its contents.
Term
Exodermis
Definition
The outermost layer of the cortex. Found in most angiosperms. Has Casparian strips.
Term
Extensins
Definition
A family of hydroxyproline-rich proteins. Strengthens the wall, making it less extensible.
Term
Fackel
Definition
A mutation in Arabidopsis that disrupts embryo development. The embryo lacks a hypocotyl. The shoot apical meristem and cotyledon are attached directly to the root.
Term
False annual ring
Definition
When more than one growth ring forms in a year.
Term
Family
Definition
The category below order and above genus. Taxa usually end in -aceae.
Term
Fascicular cambium
Definition
Vascular cambium arising within vascular bundles.
Term
Feathery moss
Definition
A growth type in mosses. Gametophytes are highly branched, plants are creeping, and sporophytes are lateral. Common in epiphytic mosses.
Term
Fertilization
Definition
A male gamete and a female gamete (both haploid) come together to form a diploid zygote.
Term
Fibres
Definition
A type of sclerenchyma cell. Generally long, slender cells that occur in strands or bundles. Varies in length from 0.8 mm to 70 mm, depending on the species. Example: hemp, jute, flax, manila hemp.
Term
Fibrous root system
Definition
Found in monocots. The primary root is short lived, and major roots arise from adventitious roots. No one root is more prominant than the others. Prevents soil erosion.
Term
Fiddlehead
Definition
The young frond of a fern. Appears in the soil tightly coiled, and unrols and expands as it grows.
Term
Filament
Definition
Part of the stamen. A slender stalk that holds up the anther.
Term
Fine roots
Definition

Feeder roots

The roots most actively engaged in the uptake of water and minerals. Occurs in the upper 15 cm of the soil, usually the richest in nutrients. Generally short lived; lasts a few months. About 33% of productivity in terrestrial ecosystems is production of fine roots.

Term
First available space
Definition
An earlier explanation for phyllotaxis. Leaves form when sufficient width and distance from the apex is attained.
Term
First node
Definition
The node where cotyledons attach to the stem.
Term
Flagella
Definition

Sinular, flagellum

A long, hair-like structure extending from the surface of many types of eukaryotic cells, about 0.2 μm in diameter. Propels the organism through water. In plants, only found on the gametes of plants with motile sperm: mosses, liverworts, ferns, cycads, and Gingko trees.

Capable of movement even when detached from the cell; movement is produced by sliding microtubule mechanisms where the outer pairs of microtubules move past one another without contracting, causing localized bending of the flagellum. Cycles of attachment and detachment between neighboring pairs in the outer ring produces regular movement. Grow from basal bodies in the cytoplasm.

Term
Flavonoids
Definition
Pigments composed of two six-carbon rings linked by a three-carbon unit. Occur in probably all angiosperms. Found in sporopollenin. Blocks UV radiation.  An anti-oxidant found in anti-aging products. Includes anthocyanins and flavonols.
Term
Flavonol
Definition
Flavonoids commonly found in leaves as well as flowers. Many are colourless. Contribute to the ivory or white hues of certain flowers.
Term
Flies
Definition
A pollinator. Attracted by the odor of dung or carrion.
Term
Flower
Definition
Found in angiosperms. Protects the ovary. Attracts specific animal pollinators, and selects for good mates. Attracts using visual and/or olfactory lures. Pollinators include pollen beetles, carrion flies, bees, butterflies, hummingbirds, and bats.
Term
Follicle
Definition
A dehiscent dry simple fruit. Derived from a single carpel that splits along one side at maturity. Example: columbine, milkweed, magnolia.
Term
Fontinalis dalecarlica
Definition
The only marine bryophytes. Lives in the Blatic Sea.
Term
Food
Definition
A use for plants. Everyting we eat directly or indirectly comes from plants. There are over 7,000 edible plant species.
Term
Food-deception
Definition
A tactic in flowers to attract pollinators. Signals the presence of a food reward, but provides none. Mimics the appearance of food-giving flowers.
Term
Foot
Definition
A component of the sporophyte of bryophytes. Attaches the seta and capsule to the archegonium of the mother gametophyte.
Term
Forisomes
Definition

"Gate-keepers"

One of the forms of non-dispersive P protein bodies. Expanded. Seals sieve tubes.

Term
Founder cells
Definition
Groups of cells in the peripheral zone of the shoot apical meristem, spanning all three layers. Forms leaf buttresses.
Term
Four-nucleate stage
Definition
The first stage in fritillaria type megagametogenesis. Three nuclei move to the chalazal end, and the remaining nucleus moves to the micropylar end.
Term
Fragmentation
Definition

Vegetative propagation

A method of asexual reproduction in bryophytes. Small pieces of tissue are separated and develop into entire, new gametes.

Term
Free central placentation
Definition
Ovules are born on a central column of tissue not partitioned into locules.
Term
Fritillaria type
Definition
A type of megagametogenesis. Occurs in Lilium. No wall formation occurs; all four megaspore nuclei participate in the formation of the embryo sac. Has two stages: four-nucleate stage and second four-nucleate stage. A pentaploid primary endosperm nucleus is formed.
Term
Fritschiella
Definition
A branhced, multicellular filamentous chloropyte. The most complex chlorophyte; has specialized cells for function and position in the body. Have subterranean rhizoids, a prostate system at soil surface, and primary and secondary branches.
Term
Frond
Definition
The leaves of ferns. There is high diversity in fronds, compared to horsetails.
Term
Fruit
Definition
Develops from the ovary and sometimes accessory tissue of the flower. For seed dispersal: wind, water, or animal-borne. This is a fundamental aspect in the evolution of angiosperms. Includes simple fruits, aggregate fruits, adn multiple fruits.
Term
Fruitlet
Definition
The individual matured ovaries of an aggregate fruit.
Term
Fucus
Definition
Brown algae with gametic meiosis.
Term
Fungi
Definition
A kingdom within Eukarya.
Term
Funiculus
Definition
A stalk that bears the ovule. May arise from the placenta.
Term
Fusiform initials
Definition
A component of the vascular cambium. Long cells. Initials which produce the axial system.
Term
G0 phase
Definition
A phase after G1 phase which is sometimes skipped. A dormant state in which initials are parrested in G1. Occurs if the checkpoint at the end of G1 was not passed.
Term
G1 phase
Definition

Gap phase 1

The first stage of interphase. The cell wall ruptures as the cell enlarges. Intense biochemical activity. There is a checkpoint at the end of G1: either initiates S phase or enters G0 phase. Centriole and centrosomes are duplicated. The nucleus moves to the centre of the cell, and cytoplasmic strands anchor it within the tonoplast, forming the phragosome.

Term
G2 phase
Definition

Gap phase 2

Checks that chromosome duplication is complete and any mistakes have been replaced. Centriole duplication is completed. The preprophase band appears. Chromosomes begin to condense. There is a checkpoint at the end of G2; either arrests or goes through with mitosis.

Term
Gametangia
Definition
Structures where gametes are produced. Includes antheridia and archegonia.
Term
Gamete
Definition
A cell that unites with another gamete to produce a zygote. Differentiates from gametophytes. Haploid, single-celled stage of sporic meiosis. Either male or female: sperm or egg, respectively.
Term
Gemetic meiosis
Definition
Single-celled haploid gametes fuse to form a diploid zygote that divids and produces a diploid sporophyte, which produces gametes. The alternation of generations found in Oomycota, and green and brown algae, including Fucus.
Term
Gametophore
Definition
Rolled-up thalli that grow perpendicular to the ground and hold up the gametangia of Marchantia. Antheridiophores and archegoniophores.
Term
Gametophyte
Definition
Haploid, muticelluar stage of sporic meiosis. Either male or female. Develop from spores. Differentiate to produce gametes. In bryophytes, the gametophyte is dominant. In vascular plants the gametophyte is small and dependent on the sporophyte.
Term
Garden bean
Definition

Phaseolus vulgaris

A eudicot with epigeous germination. Food is stored in the cotyledons of the seed.

Term
Gas exchange
Definition
A use for plants. Plants absorb CO2 and release O2. This is fundamentally important to all ecosystems. 40% of the earth's carbon is tied up in plants.
Term
Gemma cup
Definition
Contains the gemmae of Marchantia. Gemmae are splashed out by raindrops.
Term
Gemmae
Definition
Multicellular bodies in bryophytes that give rise to new gametphytes by asexual reproduction. Found in gemma cups.
Term
Generative cell
Definition

One of the cells in a gymnosperm pollen grain.

In angiosperms, the smaller cell formed in two-celled stage of microgametogenesis. Divides to form the sperm cells in three-celled stage.

Term
Genemosperma
Definition
An ancient species which had integumentary lobes, rather than an integument.
Term
Genotype
Definition
The genetic constitution of an individual.
Term
Genus
Definition

Plural, genera

The category below family and above species. The first term in the binomial system. May be written by itself.

Term
Germ tube
Definition
The first structure that extends from the spores of bryophytes.
Term
Germination
Definition
Resumption of growth of the embryo after quiescence. Depends on many factors, external and internal. Temperature must be within a certain range. For most plants this is 0º - 48º C, with an optimum at 25º - 30º C. The seed must imbibe water to resume metabolic activities; it may swell and produce considerable pressure. The seed releases or synthesizes enzymes (amylases, lipases, proteinases) that digest stored foods in the seed. The seed digests seed food stores until it is established. Embryo cells enlarge and divide, requiring continuous supply of water and nutrients. Glucose breakdown is anaerobic until the seed coat is ruptured and intakes oxygen from the soil. The germination requirements of each species is adapted to its envionment: moisture, oxygen, temperature, light, stratification, scarification, water, microbial digestion, chemical digestion. Germination is epigeous or hypogeous.
Term
Gibberellic acid (G)
Definition
A plant hormone that promotes germination. Controls the activity of enzymes that digest foods stores in the seed. Synthesized in the embryo and scutellum, and moves to the aleurone layer.
Term
Ginkgophyta
Definition
A phyla within Plantae. Seed-producing vascular gymnosperms. Contains ginkgoes.
Term
GL1
Definition

GLABROUS2

Activated early in development of protoderm cells.

Term
Globular stage
Definition
The third stage in embryogenesis. The embryo proper becomes spherical. Progresses into heart stage.
Term
Glycoproteins
Definition
A component of the cell wall. Structural proteins. Includes extensins.
Term
Glyoxysome
Definition
A peroxisome that contains enzymes necessary for conversion of stored fates into sucrose during germination of many seeds.
Term
Gnetophyta
Definition
A phyla wihin Plantae. Seed-producing vascular gymnosperms. Contains gnetophytes: vessel-containing gymnosperms.
Term
Gnom
Definition
A mutation in Arabidopsis that disrupts embryo development. The embryo lacks apical-basal pattern.
Term
Golgi apparatus
Definition
A component of the endomembrane system. Produces vacuoles. Consists of Golgi bodies.
Term
Golgi bodies
Definition

Golgi stacks

Golgi dictysomes

Five to eight stacks of cisternae, often branched into complex series of tubules at the margins. Has two poles: cis face and trans face. Plants have many separate Golgi bodies. Different steps of protduction occur sequentially in each cisternae. Synthesize non-cellulose polysaccharides for the cell wall. Transform ER type membranes into vesicle type membranes. Transition vesicles deliver glycoproteins from the ER. Shuttle vesicles carry glycoproteins to subsequent cisternae. Coated vesicles package newly formed proteins.

Term
Grafting
Definition
Using roots stalk from disease- or cold-resistant crops to produce better fruit varieteis. Practiced in Canada.
Term
Grana
Definition

Singular, granum

Thylakoid complexes in chloroplasts. The thylakoids are connected by stroma thylakoids.

Term
Green algae
Definition
Evolved into the chloroplasts of land plants in the Endosymbiont Theory.
Term
Gregor Mendel
Definition
Looked at seven different traits in pea plants to study how alleles are inherited.
Term
Ground meristem
Definition
A primary meristem. The precursor of the ground tissue system. Surrounds the procambium. Originates partially from the peripheral zone, and partially from the pith meristem of the shoot apical meristem.
Term
Ground tissue system
Definition
Originates from the ground meristem. Vascular tissue is embedded in it. Surrounded by dermal tissue. Has simple tissues. In leaves it is the mesophyll. There are three tissues: parenchyma, collenchyma, and sclerenchyma.
Term
Growth
Definition
A process of development. An irreversible increase in size. Cells divide and enlarge. Cell division alone is not growth, but increases potential for growth.
Term
Growth rings
Definition
Growth increments of secondary xylem and phloem. May be hard to distinguish in tropical trees which have constant secondary growth. Wider during years with good growing conditions. Incldues annual rings and false annual rings.
Term
Guard cells
Definition

"Gatekeepers"

Specialized epidermal cells. Regulate stomata. Open and close the stomata to control movement of gases including water vapour in and out of the plant.

Term
Gurke
Definition
A mutation in Arabidopsis that disrupts embryo development. The embryo lacks a shoot apical meristem and cotyledons.
Term
Gymnosperm
Definition

"Naked", "Exposed"

A member of spermatophytse. Seed vascular plants. Includes cycadophyta, ginkgophyta, coniferophyta, and gnetophyta. The ovary is not protected by a flower. Have separate and male strobili on the same tree. Male strobili are born on lower branches than femal cones, to prevent self-fertilization.

Term
Gynoecium
Definition

"House of woman"

The carpels of a flower.

Term
Habitat
Definition
A use of plants. Plants are the backbone of all habitats. Other species depend on plants for food and shelter.
Term
Hadrom
Definition
A central stand of hydroids in true mosses. Water-conducting tissue, analogous to xylem, but lacks lignified wall thickenings.
Term
Halimeda
Definition
A member of Codium. Have calcified cell walls that play a role in the formation of white carbonite sands of many tropical waters. Produces a metabolite that reduces feeding by herbivorous fish. Grows rapidly at night, building up toxic compounds. The chloroplasts move to the outside only in the day.
Term
Haploid (n)
Definition

"Single set"

With one copy of genes.

Term
Hardwood
Definition
Wood from angiosperms. Has vessles, and is extremely varied. Average of 17% of the wood volume is rays.
Term
Heart stage
Definition
The fourth stage of embryogenesis. The dicot emrbyo forms two lobes. The monocot embryo becomes cylindrical. Cotyledons develop. May begin during or after procambium becomes discernible. The axisis partitioned into shoot apical meristem, cotyledons, hypocotyl, radicle, and root apical meristem.
Term
Heartwood
Definition
Older, non-conducting wood which has lost reserve foods. May be filled with substances that colour it/and or make it aromatic: oils, gums, resins, tannins. Often darker in colour. Allows the plant to accumulate toxic secondary metabolites away from living cells.
Term
Hemicellulose
Definition
A component of cell walls. Characteristic of cells which are no longer growing. Varies greatly between cell types and plant species. Hydrogen-bonded to cellulose microfibrils, tethering them together. Limits the size of the cell.
Term
Herbaceous
Definition
Undergoes little or no secondary growth. Non-woody. Many eudicots are herbaceous.
Term
Heredity
Definition
An attribute of living things. The ability to pass on characteristics to subsequent generations.
Term
Heteromorphic
Definition
When the haploid and diploid forms of an alternation of generations are not identical, due to mutations and interactions between genes. Found in plants, and some green and red algae.
Term
Heterosporous
Definition
Producing two types of spores, which develop into unisexual gametophytes. Found in later vascular plants.
Term
Heterotroph
Definition

"Other feeder"

Satisfy their energy requirements by consuming organic compounds produced by external sources. Dependent on outside sources of organic molecules for energy. Evolved before autotrophs, and fed on organic molecules. The evolution of autotrophic organisms allowed for energy flow into the biosphere. Includes animals, fungi, and many types of bacteria.

Term
Heterozygous
Definition
Individuals with two different alleles.
Term
Hilum
Definition
A small pore in the seed coat, the remnants of the micropyle after the seed has separated from the funiculus.
Term
Homeotic genes
Definition
Genes that affect floral organ identity. Studied in Antirrhinum and Arabidopsis. Usually MADS box genes.
Term
Homeotic mutations
Definition
Mutations that result in formation of the wrong organ in the wrong place. Used to study the genetic control of flower development. Includes double flowers.
Term
Homologous structures
Definition

"Agreement"

Structures with a common evolutionary origin, but not a common function.

Term
Homosporous
Definition
Producing one type of spores, which develop into bisexual gametophytes. Found in early vascular plants.
Term
Homozygous
Definition
Individuals with two identical alleles.
Term
Hook
Definition
A structure formed in germinating seedlings. In epigeous eudicots it is the hypocotyl. In hypogeous eudicots it is the epicotyl. In smaller monocots it is the cotyledon.
Term
Hyaline cells
Definition
Large dead cells in the ring-like spiral wall thickenings of the leaves of sphagnum moss. Have high water-holding capacity, and give peat moss its great ability to hold up to 20 times its dry weight in water. Cyanobacteria may live inside hyaline cells.
Term
Hydrodictyon
Definition

Water-nets

A multicellular non-motile chlorophyte. Can form massive blooms in ponds, lakes, and streams. A large, cylindrical cell arranged in a lacy, holly cylinder shaped net. Reproduce asexually by forming uninucleate, biflagellated zoospores which become components of daughter nets. Sexual reproduction is isogamous with zygotic meiosis.

Term
Hydroids
Definition
Elongated cells with ends permeable to water. Found in the hadrom of mosses. Living cells with degenerate nuclei.
Term
Hydrophytes
Definition
Plants that require a large supply of water, or grow in water. Submerged surfaces usually completely lack stomata. Often floats in water due to large intercellular spaces between spongy parenchyma. Vascular tissue is much reduced.
Term
Hydrotropism
Definition
Tropism in response to water. Roots extending towards water.
Term
Hypanthium
Definition
A short tube formed by perianth and stamens being adnate to the calyx in perigynous flowers. Arises from the base of the ovary. Example: cherry blossoms.
Term
Hypertonic
Definition
High salt concentration. Sucks water out of cells.
Term
Hypocotyl
Definition
The stem-like axis below the cotyledons. Attaches to the radicle at the hypocotyl-root axis.
Term
Hypocotyl-root axis
Definition
Where the hypoxotyl attaches to the radicle. When the radicle cannot be distinguished in the embryo, it refers to the axis below the cotyledons.
Term
Hypogeous germination (eudicots)
Definition
The epicotyl elongates and forms the hook that pulls the shoot tip and young leaves through the soil. Cotyledons remain under the soil and decompose after food stores are depleted. Example: peas.
Term
Hypogynous flower
Definition
The perianthe and stamens are situated on the receptacle beneath the ovary. Example: lilies
Term
Imperfect flowers
Definition

Unisexual flowers

Either stamens or carpels are missing. Incomplete. Either staminate or carpellate.

Term
Incomplete flowers
Definition
Flowers that lack one or more of the four floral organs: sepals, petals, stamens, or carpels. Includes imperfect flowers.
Term
Indehiscent
Definition
Dry simple fruits that do not split open at maturity. Usually originate from an ovary with only one seed, but more than one ovule may be present. Includes achenes, cypselas, caryopsis, nuts, and schizocarps.
Term
Indeterminate
Definition
Continuously growing. Plants grow for their entire lives.
Term
Indusium
Definition
A small membrane covering sori on some ferns.
Term
Inferior flowers
Definition
The calyx, corolla, and androecium attach near the top of the ovary. Protects the ovary from predation by insects.
Term
Ingroup
Definition
The taxon under investigation.
Term
Inhibitory field hypothesis
Definition
An explanation for phyllotaxy. Pre-existing leaf primordia inhibit the formation of new leaves in their immediate vicinity.
Term
Inflorescence
Definition
A cluster of flowers.
Term
Initials
Definition
Cells that maintain the ability to divide. Divide so that one daughter cell remains in the meristem, and the other becomes a derivative.
Term
Inner bark
Definition
Bark tissues inside the innermost cork cambium. Live tissues.
Term
Integument
Definition
A component of an ovule: a layer around the megasporangium. Develops into the seed coat. Has a small opening, the micropyle. Evolved through gradiual fusion of integumentary lobes, until only the micropyle was left.
Term
Intercalary meristem
Definition
At the base of the internode. A localized region of elongation in the internode between two highly differentiated regions.
Term
Interfascicular cambium
Definition
Vascular cambium arising in interfascicular regions or pith rays.
Term
Interfascicular regions
Definition

"Between the bundles"

Cambium. Parenchyma cells that interconnect the cortex and pith.

Term
International Code of Botanical Nomenclature
Definition
Consists of the rules governing the scientific naming of plants, photosynthetic protists, and fungi.
Term
International Code of Nomenclature of Bacteria
Definition
Contains the rules governing the scientific naming of microbes.
Term
International Code of Zoological Nomenclature
Definition
Contains the rules governing the scientific naming of animals, non-phososynthetic protists, and fungi.
Term
Internode
Definition
A component of a phytomere. Increase the length of the stem by elongation. Elongation may occur as a wave, or be resistricted to the intercalary meristem.
Term
Interphase
Definition
One of the phases of cell cycle. Intense cellular activity and preparations for cell division. Chromosomes are duplicated, organelles doubled, structures for cell division produced. Most cells have endoreduplication. Has three phases: G1, S, and G2.
Term
Intine
Definition
The inner wall of a pollen grain. Composed of cellulose and pectin.
Term
Inverted repeats
Definition
Areas in the chloroplast genome that encode the same gene, but in opposite directions (the genome is circular).
Term
Iodine potassium iodide (I2KI)
Definition
A stain that stains starches blue/black.
Term
Isomorphic
Definition
When the haploid and diploid forms of an alteration of a generation are identical. Found in most red algae, many green algae, and a few brown algae.
Term
Jacket layer
Definition
A sterile component of an antheridia. Surrounds the spermatogenous tissue.
Term
Judean Date palm
Definition

Pheonix dactylifera

The oldest known viable seeds. Approximately 2000 years old. Seeds were found at an archaeological site in 2005. The tree was dioecious, so the species was lost. 

Term
Karl C. Hammer and James Bonner
Definition
Studied photoperiodism in cocklebur.
Term
Karyogamy
Definition
The fusion of the nuclei of two zoospores.
Term
Kinetochore
Definition
A protein complex which develops on either side of a centromere. Attaches to kinetochore microtubules.
Term
Kinetochore microtubules
Definition
Spindle fibres which are attached to kinetochores. Extend to opposite poles from the sister chromatids of each chromosome. Move chromosomes to the equatorial plane of the mitotic spindle.
Term
Klebsormidium
Definition
A freshwater, unbranched, filamentous charophyte.
Term
Kingdom
Definition
The category beneath domain and above phyla.
Term
Konstantin Mereschkowski
Definition
Postulated the Endosymbiotic Theory in 1910.
Term
Kranz anatomy
Definition

"Wreath"

Two concentric layers of large parenchyma cells with large chloroplasts that form the bundle sheath of C4 plants. The veins conduct photosynthates more rapidly.

Term
Lacunar
Definition
An organization of collenchyma cells. A hybrid of angular and lamellar. There are intercellular spaces.
Term
Lamellar
Definition
An organization of collenchyma cells. Cells are arranged in ordered rows, thickened at the tangential face of the cell wall. Thickened in strips.
Term
Late wood
Definition
Older wood that is more dense, with narrower cells and proportionally thicker walls.
Term
Lateral meristem
Definition
Meristems of the vascular cambium and cork cambium. Produce secondary growth.
Term
Lateral root
Definition
Branching roots. Roots that develop from the primary root, or adventitious roots. In a taproot system, older lateral roots are found closer to the base of the plant.
Term
Lateral rootcap
Definition
A component of the root cap. The lateral portion which surrounds the columella.
Term
Leaf
Definition
A component of a phytomere. The main photosynthetic organs. Water moves through the leaves. There are two types: microphylls and megaphylls. Develop from leaf primordia.
Term
Leaf buttress
Definition
A bulge in the founder cells which develops into a leaf primordia. Flatter on the upper surface than on the lower surface.
Term
Leaf primordia
Definition
Develop into leaves.
Term
Leaf sheath
Definition
Surrounds the stem; wraps around another sheath, or hte stem. Found in monocots and eudicots. Common in grasses.
Term
Leaf trace
Definition
Extensions of the vascular system that grow towards leaves. A single leaf may have one or more leaf traces. Vary in length. Extends from the stem bundle.
Term
Leaf trace gap
Definition
Wide interfascicular regions of ground tissue in the vascular cylinder located above where leaf traces diverge.
Term
Leaflet
Definition
The individual blades of a compound leaf.
Term
Leafy liverworts
Definition
A type of liverword. 4000 species, abundant in the tropics and subtropics in humid forests, on the bark and leaves of trees. "Leaves" are equal in size, spirally arranged around the stem, and lack a midrib structure. They may be highly lobed or dissected, and are arranged in two rows of equal-sized leaves along opposite sides of a stem, with a third row of underleaves along the lower surface. Antheridia are held on androecia. Archegonia are surrounded by the perianth.
Term
Leafy mutation
Definition
A mutation in Arabidopsis that results in leaves in all whorls. Caused by loss of class E genes.
Term
Leefructus mirus
Definition
The oldest eudicot. Fossils found in China. 125 million years old. A member of the buttercup family.
Term
Legume
Definition
A dehiscent, dry simple fruit. Characteristic to the pea family. A single carpel that splits along both sides at maturity.
Term
Lenticel
Definition
Portions of the periderm with loosely arranged cells and intercellularspaces. Provides aeration of internal tissues. Forms during the development of the periderm, generally below a stoma or group of stomata. Raised circular, oval, or elongated areas. May form on some fruits. Develop at the bottom of cracks in bark.
Term
Lepidodendron
Definition
An extinct plant that dominated hot, humid swamps in the Carboniferous Period. It was up to 35 m tall, with sparse branching, no roots, and an inefficient vascular system. They were not stable and often fell over. They depended on water for reproduction. They were not good at getting water from ground water, but fixed huge amounts of carbon from the atmosphere, leading to climate change, and contributing to coal deposits.
Term
Leptoid
Definition
Cells that form the leptom in true mosses. Living cells with degenerate nuclei.
Term
Leptom
Definition
A stand of leptoids in true mosses. Food-conducting tissue that surrounds the hadrom, analogous to phloem.
Term
Leucoplast
Definition
A plastid. Lacks pigment and inner membrane systems. Includes amyloplasts.
Term
Life
Definition
Has the ability to grow and reproduce, heredity, and cellular organization.
Term
Lignin
Definition
A step in the evolution of vascular plants. A component of the cell wall. Adds compressive strength and stiffness to cells. Found in the cell walls of structurally supportive tissues. Makes it possible for the sporophyte to reach tall structures. Not easily digestesd by animals.
Term
Lipase
Definition
An enzyme released in the seed that digests stored starches.
Term
Locules
Definition
Partitions of an ovary, especially if carpels are fused. The number of locules is related to the number of carpels.
Term
Locus
Definition
A specific location on a chromosome.
Term
Long-day plants
Definition

Short-night plants

Flower in the summer. Need a light period longer than a critical length to flower. Example: spinach, potatoes, wheat, lettuce, henbane.

Term
Lumen
Definition
Inside the ER. Continuous with the nuclear envelope.
Term
Lycopodiophyta
Definition
A phyla within Plantae. Seedless tracheophytes. Contains lycophytes: club mosses, spike mosses, and quillworts. Dominated the Late Devonian period through to the Carboniferous Period. The oldest living vascular plant divison (410 million years old). Habitat spands from the Arctic to the tropics. Homosporous: spores produced in sporophylls are grouped into strobili. Require water for fertilization: biglagellate sperm swim to the archegonium. Gametophytes are subterranean and require symbiotic relationship with mycorrhizal fungus for normal growth.
Term
Macrofibrils
Definition
Bundles of micelles. Forms the cell wall.
Term
MADS box gene
Definition
Homeotic genes that control aspects of flower development.
Term
Magnoliaceae
Definition
The first clade to diverge from Mesangiospermae. Flowering parts are numerous and spirally arranged. Leaves produce ethereal oils, creaging a distinctive scent. Laurels, Piperales, and Canellales. Generally resitricted to Australasia.
Term
Major veins
Definition

Mature veins

Large veins associated with the midrib. Collect photosynthates from minor veins and transport them out of the leaf. Develop upward into the leaf as an extension of the leaf trace.

Term
Male germ unit
Definition
The two sperm cells and vegetative nucleus of a germinated pollen grain.
Term
Marchantia
Definition
A group of complex thalloid liverworts. Grows on moist rocks and soil. Unisexual. Gametangia are held on gametophores: antheriophors and archegniophores. Spores are surrounded by elaters which disperse spores. Gemmae are found in gemma cups.
Term
Marchantiophyta
Definition

Liverworts

About 5200 species of bryophyts. Some are thalloid. Reproduce sexually by producing antheridia and archegonia on separate male and female plants. It was once believed that they would aid in diseases of the liver because some speices resemble the human liver in shape. Probably the closest living relatives to the first land plants. Many form symbiotic relationships with glomeromycetes. Produce mucilage which aids in water retention. There are three types: complex thalloid, leafy, and simple thalloid.

Term
Marginal meristem
Definition

Marginal blastozone

Bands of dense cells on either side of the leaf primordium, which develop into the blade of the leaf.

Term
matK
Definition
A barcode gene for plants, but can be supplemented with additional markers as required. Works better for some plants than others.
Term
Matrix
Definition
Inside theh inner membrane of a mitochondria. Contains proteins, RNA, DNA, small ribosomes, and various solutes.
Term
Matrotrophy
Definition

"Food derived from the mother"

Fluid supplied to the zygote in archegonia of bryophytes. Sugars, amino acids, and other substances. Helps the embryo grow.

Term
Maturation phase
Definition
The stage following embryogenesis in seed development. Build-up of food reserved (starch, proteins, oils) in the endosperm, perisperm, and/or cotyledons. The seed undergoes desiccation, and may enter a quiescent state. Metabolism in the seed decreases to an imperceptible level.
Term
Medicines
Definition
A use of plants. Vaccines, anti-cancer drugs, therapeutic proteins. 25% of prescription drugs come directly or indirectly from plants.
Term
Megagametogenesis
Definition
Development of the embryo sac from a megaspore. Occurs after megasporogenesis. There are three types: polygonum, fritillaria, and oenothera.
Term
Megagametophyte
Definition
The female gametophyte in vascular plants. The embryo sac. Arise from megaspores.
Term
Megaphyll
Definition
A type of leaf. Larger than microphylls. Contains a complex system of branchign vascular tissue. Found in ferns and seed-plants.
Term
Megasporangia
Definition
In megasporophylls of spike moss.
Term
Megasporangiate
Definition
The female strobili of a gymnosperm. Has seed-scale complexes. The ovule is exposed and vulnerable to infection, desiccation, and herbivory. Screening of a mate is not easy. If the embryo is lost, energy is wasted.
Term
Megasporangium
Definition
A component of an ovule. The structure where megaspores are produced.
Term
Megaspore
Definition
Gives rise to megagametophytes in vascular plants. Four arise in the megasporocyte in the megasporangium and three disintegrate.
Term
Megasporocyte
Definition

Megaspore mother cell

Surrounded by the nucellus. Undergoes meiosis, giving rise to four megaspores.

Term
Megasporogenesis
Definition
The megasporocyte undergoes meiosis and forms 4 haploid megaspores in a tetrad formation. Occurs in the nucellus.
Term
Megasporophyll
Definition
Contain megasporangia in spike moss.
Term
Meiosis
Definition
A diploid cell gives rise to four genetically different haploid cells: gametes or spores. Occurs in specialized diploid cells at particular times in the life cycle of organisms. A form of genetic recombination: contributes to genetic variation by recombining chromosomes, and through crossing over. Consists of two divisions: meiosis I and II.
Term
Meiosis I
Definition
The first division in meiosis. Homologous chromosomes pair and separate from one another. The chromosomes have already duplicated during interphase. Each homolog is derived from a different parent, and is made of two identical chromatids. Consists of prophase I, metaphase I, anaphase I, and telophase I.
Term
Meiosis II
Definition
The second division in meiosis. Chromatids of each homolog separate. Sister chromatids are still attached at the centromeres. Meiosis II resembles mitosis.
Term
Meristem
Definition

"Division"

The location of most plant development after embryogenesis. Regions that retain the potential to divide; capable of adding cells indefinately to the plant body. Includes the apical and lateral meristems.

Term
Meristematic cap
Definition
Responsible for expansion of the apical region into a wide crown. Below young leaf bases. Localized cell divisions result in formation of procambial strands. Most meristem responsible for stem thickening is below the meristematic cap.
Term
Mesocarp
Definition
The middle layer of the pericarp. May be absent.
Term
Mesocotyl
Definition
The first node of grass seedlings.
Term
Mesophyll
Definition
The ground tissue of leaves. As large intercellular spaces which are aerated by the stomata, facilitating rapid gas exchange. Numerous chloroplasts. Specialized for photosynthesis. Two cell types; palisade and spongy parenchyma. In some grasses, there is no distinction between two cell types.
Term
Mesophytes
Definition
Plants that require an environment which is neither too wet nor too dry.
Term
Mesostigma
Definition
A unicellular, freshwater, scaly flagellate charophyte.
Term
Mestome
Definition
The inner sheath of the bundle sheath in C3 grasses. Consists of thick-walled cells.
Term
Metaphase
Definition
The second phase of mitosis. Begins when the mitotic spindle forms. Ends when kinetochore microtubule filaments have moved all the chromosomes to the metaphase plate.
Term
Metaphase I
Definition
The second stage of meiosis I. The spindle becomes conspicuous, microtubules attach to centromeres of bivalents and move them to the equaotrial plane where they line up randomly.
Term
Metaphase II
Definition
The second stage of meiosis II. The spindle becomes conspicuous, chromosomes line up with centromeres at the equatorial plane.
Term
Metaxylem
Definition

"Later xylem"

Primary xylem that differentiates after protoxylem occupies inner portions of the ridges and centre of the vascular cylinder.

Term
Micelles
Definition
Bundles of microfibrils wound together. Arranged into macrofibrils.
Term
Microfibrils
Definition
Bundles of cellulose fibres. 10 - 25 nm in diameter. Synthesizes by cellulose synthase. Wind together to form micelles.
Term
Microgametogenesis
Definition
The development of microgametophytes (pollen grains) from microspores. Occurs after microsporogenesis. The microspore divides twice: in two-celled stage it forms the vegetative and generative cells, in three-celled stage the generative cell divides to form two sperm cells.
Term
Microgametophyte
Definition
The male gamete in vascular plants. Pollen grains. Arise from microspores.
Term
Microphyll
Definition
A type of leaf. Smaller than megaphylls. Contain a single strand of vascular tissue. Found in lycophytes.
Term
Microphylar end
Definition
The end of the embryo sac near the micropyle. The egg apparatus (egg cell and two synergids) are at this end.
Term
Micropyle
Definition
A small opening in the integuments of the ovule.
Term
Microsporangia
Definition
Born on microsporophylls in spike moss. The site of microsporogenesis in the anther. Contain sporogenous cells that develop into microsporocytes.
Term
Microsporangiate
Definition
The male strobili of gymnosperms. Smaller than a megasporangiate. Contains many microsporocytes that produce pollen grains.
Term
Microspore
Definition
Gives rise to microgametophytes in vascular plants. Four arise from the microsporocytes that produce pollen grains.
Term
Microsporocytes
Definition

Microspore mother cells (SMC)

Undergo meiosis to produce four microspores. Develop a layer of callose, which is digested by callase from the tapetum, breaking the connections between neighboring microsporocytes.

Term
Microsporogenesis
Definition
The formation of microspores via meiosis. Occurs in microsporangia.
Term
Microsporohylls
Definition
Inside microsporangia in spike moss.
Term
Microtubule
Definition
A component of the cytoskeleton. Cylindrical structures 24 nm in diameter. Built of tubulin subuits arranged into 13 protofilaments. All subunits are arranged with the same polarity. Has a fast growing plus end and a slow growing minus end. Has dynamic alignment of cellulose microfibrils as they are added to the cell wall. Found in flagella.
Term
Microtubule organization centre
Definition
Nucleating sites in teh cortical cytoplasm, and at the surface of the nucleus. Where microtubules are assembled.
Term
Middle lamella
Definition
The intercellular substance between the primary cell walls of neighboring plant cells. Contains pectins. Includes pit membanes.
Term
Midrib
Definition
The largest vein on the axis of the leaf. Occurs in an enlarged portion of the blade, extending from the lower surface of the blade.
Term
Minor veins
Definition

Small veins

Veins completely embedded in mesophyll tissue. Collect photosynthates from mesophyll. Develop starting from the tip of the leaf. Enclosed in a bundle sheath.

Term
Mitochondria
Definition

Singular, mitochondrion

A component of the cytoplas. Has two membranes. Smaller than plastids: about 0.5 μm in diameter, with great variation in length and shape. The site of respiration, producing ATP. Synthesizes amino acids, vitamin cofactors, and fatty acids. Plays a role in programmed cell death. Aggregate in the cell in areas where energy is required. The inner membrane has cristae enclosing a matrix. Replicated by binary fission. Has a nucleoid with DNA, and can code for some of its own polypeptides. Evolved from an endosymbiont that was originally an alpha-proteobacterium that was engulfed by a heterotrophic phagocyte. The aerobic bacteria's ability to perform respiration helped the host phagocyte, allowing it to thrive in oxygen-rich environments. Eventually the baceteria evolved into mitochondria.

Term
Mitosis
Definition

"Thread"

The first phase of cell division. Nuclear division. Nuclear division. A complete set of chromosomes, and cytoplasm are allocated to each daughter cell nuclei. The duration of mitosis differs between organisms and cell type. Has four main phases: prophase, metaphase, anaphase, and telophase.

Term
Mitotic spindle
Definition
A structure that forms in metaphase. Widest in the centre and tapered towards the poles. Appears where the nucleus used to be. Consists of spindle fibres.
Term
Monilophyta
Definition

Pteridophyta

A phyla within Plantae. Seedless tracheophyts. Contains ferns, whisk ferns, and horsetails.

Term
Monocot
Definition

Monocotyledons

Flower parts in a multiple of three. Monoaperturate: have one pore or furrow on the pollen. One cotyledon. Usually parallel leaf venation. Scattered arrangement vascular bundles in the stem. Secondary growth with vascular cambium in rare. Example: grasses

Term

Monoecious

"Single house"

When both staminate and carpellate flowers occur on the same plant.

Definition
Term
Monohybrid cross
Definition
A cross between individuals that differ in a single trait.
Term
Monophyletic group
Definition

Clade

An ancestor, plus all of its descendants. Can be removed from the phylogenetic tree with one "cut". Every taxa is a monophyletic group, but not every monophyletic group is a taxa.

Term
Monopteros
Definition
A mutation in Arabidopsis that disrupts embryo development. The embryo lacks a root.
Term
Motor proteins
Definition
Use ATP to pull chromosomes along kinetochore microtubules. Includes dynein and kinesin.
Term
Morphogenesis
Definition

"Shape origin"

A process of development. The plant assumes a particular shape. Determined by the planes in which cells divide and expand.

Term
Mucigel
Definition
Released by the root cep. Lubricates the soil.
Term
Mucilage
Definition
A highly hydrated polysaccharide that lubricates the root during its passage through the soil. Secreted by the border cells.
Term
Mucilage sheath
Definition
Carbon-rich materials produced by sloughed off broder cells in the soil.
Term
Multiple fruit
Definition
A type of fruit. Derived from an inflorescence that is from the combined gynoecia of many flowers. Example: fig, mulberry, pineapple.
Term
Myco-heterotrophic
Definition
Plants that lack chlorophyll, are non-photosynthetic, and have obligate relationships with mycorrhizal fungi which transfer carbohydrates from a host plant to the myco-heterotrophic plant.
Term
Mycorrhizal fungus
Definition
Forms a symbiotic relationship with Lycophyta which is necessary for normal growth.
Term
Natural classification
Definition
Systems of classification based on the phylogeny of organisms. Often begins with phylogenic trees.
Term
Natural resources
Definition
A use of plants. Fuel, wood, rubber, industrial biorenewables.
Term
Neck canal celsl
Definition
A component of archegonia. Disintegrates when the egg is mature, creating a fluid-filled tube through which sperm can swim towards the egg.
Term
Nectar
Definition
A sweet sugary liquid secreted by the nectaries of certain flowers. Attracts and rewards animal pollinators. Often it is fragant.
Term
Nectar guides
Definition
Colour patterns, grooves, or rows of trichomes that lead the pollinator towards the nectary of a nectar-producing flower.
Term
Nectary
Definition
A nectar-secreting structure or tissue; may be formed on or within tissues of the four floral organs, or between any two whorls.
Term
Netted venation
Definition

Reticulate venation

Found in most angiosperms other than monocots. Veins are branched with successively smaller veins branching from larger ones.

Term
Nocturnal moths
Definition
A pollinator. Flowers are white or pale in colour.
Term
Node
Definition
A component of a phytomere. Includes the first node and second node.
Term
Non-conducting phloem
Definition
Phleom which is dead. Parenchyma cells in the rays and inner bark. Function in storage.
Term
Non-dispersive P protein bodies
Definition
Large bodies of P protein in sieve tubes of some legumes, which doesn't disperse on walls. Undergoes rapid and reversible calcium-controlled changes from resting stage in forisomes.
Term
Nonvascular
Definition
Lack water-conducting vessles, xylem and phloem. Bryophytes are nonvascular. Short-statured plants, in aquatic or semi-aquatic habitats. Must be in contact with water to reproduce. Most tissues absorb water as needed. Structural support is support is provided by the habitat.
Term
Nostoc
Definition
Filamentous cyanobacteria that infect hornworts and form symbiotic relationships, living in mucilage-filled cavities, fixing nitrogen in exchange for protection and nutrients.
Term
Nuclear-type
Definition
A type of endosperm development. The endosperm has free-nuclear divisions before cell wall formation.
Term
Nucellus
Definition
Surrounds the megasporocyte in megaporangiates in gymnosperms. In angiosperms it is the megasporangium where megasporogenesis occurs. Can form the perisperm.
Term
Nuclear envelop
Definition
A double membrane with pores where the inner and outer membranes are joined. Allows for exchange of materials between the nucleus and cytoplasm. Its internal space is continuous with the lumen of the ER. It may have polysomes attached to it.
Term
Nuclear genome
Definition
The DNA found in the nucleus.
Term
Nucleoid
Definition
A clear, grana-free region of the chloroplast, or mitochondria, where DNA is found.
Term
Nucleolus
Definition

Plural, nucleoli

A region of the nucleus with a high concentration of RNA, proteins, and loops of DNA emanating from several chromosomes. The sites of formation of rRNA which are transferred to the cytosol through nuclear pores.

Term
Nucleoplasm
Definition
The nuclear matrix inside the nuclear envelope.
Term
Nucleus
Definition
A component of the cytoplasm. The most prominent structure. Present only in eukaryotes. Enables increased quantities of DNA. Controls ongoing activities of the cell by determining when and what proteins are produced. Stores genetic information of the nuclear genome. Consists of the nuclear envelope, nucleoplasm, chromatin, and the nucleolus.
Term
Nut
Definition
An indehiscent, dry simple fruit. The pericarp is hard and stony throughout. Usually develops from a compound ovary with one functional carpel. Generally has one seed. Example: acorn, hazelnut.
Term
Nymphaeales
Definition

Water lilies

A basal grade angiosperm. Evolved from land plants. Adapted to high light intensity.

Term
Oedogonium
Definition
An unbranched, filamentous chlorophyte. Attached to substrate, but can detach into water. Forms "caps", annual scars with each cell division.
Term
Oenothera type
Definition
A type of megagametogenesis. Four cells and four nuclei at maturity: the egg apparatus (egg cell, two synergids), and a uninucleate central cell. A diploid primary endosperm nucleus is formed. Occurs in Autrabaileyals and Nymphaeales.
Term
Oil body
Definition
Spherical droplets of starch and lipids sometimes found in chloroplasts. Not an organelle because it lacks a membrane. Produced in the ER and are released into the cytosol. Temporary storage of energy when the chloroplast is active. Not found in plants that have been in the dark for extended periods. Most abundant in fruits and seeds. 45% of the weight of a sunflower, peanut, flax, or sesamy seed is oil bodies.
Term
Oligosaccharins
Definition
A component of cell walls. Can function as a signal molecule.
Term
Onion
Definition

Allium cepa

A monocont with simple germination: forms a hook

Term
Oomycota
Definition
Protist water mould that has gametic meiosis.
Term
Open meristem
Definition
It is not possible to distinguish between the root cap and root body; they originated from a shared initial.
Term
Open stigma
Definition

Hollow stigma

A stigma lined by glandular epidermis on which the pollen tube grows.

Term
Open type
Definition
A type of apical organization of roots. All regions in the root (or at least cortex and root cap) arise from one group of initials.
Term
Open vascular bundles
Definition
Do not give rise to cambium.
Term
Operculum
Definition
A round lid which covers the capsule of sphagnum moss. When pressure builds up in the capsule, it is blown off, and spores are dispersed.
Term
Opposite
Definition
A phyllotaxy. Leaves are in pairs at each node. Example: maple, honeysuckle.
Term
Orbicules
Definition
Granules rich in lipids, containing sporopollenin. Produced by the tapetum.
Term
Orchidaceae
Definition
One of the most specialized and the most numerous family of flowers. Monocots. 24,000 species, mostly tropical. Three carpels are fused. Inferior ovary. Each ovary contains thousands of ovules; each pollination even produces many seeds. There is one stamen, fused with the carpel to form the column. The anthers are together as a unit in the pollinium. Three petals: two lateral wings, and one cup-like lip, often large and showy. Sepals are showy. The flower has bilateral symmetry. Varies in size from a pin-head to over 20 cm in diameter .Some orchids are myco-heterotrophs. Vanilla is an orchid.
Term
Order
Definition
The category under class and above family. Taxa usually end in -ales.
Term
Organizing centre
Definition
A small zone in the central zone beneath the L3 layer where WUS genes are expressed.
Term
Outer bark
Definition
Tissues outside the innermost cork cambium: periderm, cortical and phleom tissues. Separated from water supply by the cork layer. Consists only of dead tissues.
Term
Outgroup
Definition
A taxon that is cloesly related to, but not a member of, the ingroup.
Term
Ovary
Definition
Part of the carpel. The lower section; encloses the ovules. If carpels are fused it may be partitioned into locules.
Term
Ovule
Definition
Consists of megasporangium, an integement, and a micropyle. Born on the funiculus. For ovule development in the ABCDE model, class C, D, and E function is needed.
Term
Ovuliferous scale
Definition
A component of the seed-scale complex. The ovule sits on top, and the sterile bract below.
Term
Oxygen in the atmosphere
Definition
700 million years ago, autotrophs increased in number, and the atmospheric oxygen levels increased a significant amount. It approached modern day levels. This resulted in some of the oxygen converting into ozone, creating the ozone layer, allowing organisms to survive on the land. It also led to more efficeint oxygen utilization in heterotrophs, respiration.
Term
Ozone
Definition

O3

A gas in the atmosphere that protexts organisms from the sun's harmful UV radiation: sub-40 nm wavelengths. The ozone layer developed 700 million years ago when oxygen levels went up to to autotrophs. This allowed organisms to live near the surface of the water, and on land.

Term
P-protein
Definition

Phloem protein

"Slime"

Found in the protoplasts of sieve-tube elements of most angiosperms. Elongate and disperse, distributing along the walls, or exist as non-dispersive P-protein bodies. Accumulate as slime plugs.

Term
Palisade parenchyma
Definition
A type of cell of the mesophyll. Columnar cells, with the long axis perpendicular to the surface of the epidermis. Most of the vertical walls are exposed to intercellular spaces. More numerous chloroplasts than spongy parenchyma. Usually located on the upper side of the leaf.
Term
Palmate
Definition
A type of compound leaf. Leaflets arise from the end of the petiole.
Term
Pappus
Definition
A structure formed form the sepal of asteraceae flowers. Aids in wind dispersal, or is barbed and attaches to passing animals.
Term
Parallel venation
Definition

Striate venation

Found in most monocots. Veins are parallel and almost equal in size, or with larger veins alternating with smaller veins. Converge at the tip of the leaf, and are interconnected by very small transferse veins.

Term
Paraphyletic group
Definition
A common ancestor, but not all of its descendants. Not given a formal name.
Term
Parenchyma cells
Definition
The constituent of parenchyma tissue. Vary in size and shape. Includes transfer cells.
Term
Parenchyma tissue
Definition
A tissue present in the ground tissue system. The most common ground tissue in plants. Composed of parenchyma cells. Found in the cortex, pith, leaf mesophyll, and the fleshy of fruits. Occurs in stands in primary and secondayr vascular tissues. Occurs inr ays in secondary vascular tissues. Alive at maturity. Retains its ability to divide. Plays a role in wound healing. Initiates adventitious strcutures. Functions in photosynthesis, storage, secretion, and movement of water and food substances. Includes chlorenchyma and companion cells of the phloem.
Term
Parietal placentation
Definition
Ovules are borne on the ovary wall, or extensions of it.
Term
Parthenium argentatum
Definition

Guayule

A flowering shrub native to southwestern US and Mexico. Forms natural rubber in its parenchyma cells: hypoallergenic latex that does not cause allergic reactions.

Term
Parthenocarpic fruit
Definition
Fruit that develop without fertilization and seed development. Especially in species with many ovules: bananas, citrus, pumpkin, fig, pineapple.
Term
Passage cells
Definition
Endoddermal cells that are thin-walled, but retain Casparian strips for prolonged periods. May eventually become suberized and deposit additional cellulose.
Term
Peas
Definition

Pisum sativum

A eudicot with hypogeous germination.

Term
Pectin
Definition
A component of the cell wall. Characteristic of the primary wall and middle lamella. Characteritsic to growing cells. Cements teh walls of neighboring cells together. Has hydrophyllic polysaccharides, attracting water making the cell wall plastic, allowing it to expand. Growing cells have 65% water in the cell wall due to pectin.
Term
Pedicel
Definition
The stalk of an individual flower within an inflorescence. Important in pumpkins, to get the perfect "lid" for jack-o-lanterns.
Term
Peduncle
Definition
The stalk of a solitary flower, or of an inflorescence.
Term
Pelargonidin
Definition
Anthocyanins that produce a red colour.
Term
Perennial
Definition
Plants which have life spans greater than one year. The stem can become thickened and woody and covered with periderm. Woody perennails cease growing in the winter. Herbaceous perennails survive the winter as underground roots, rhizomes, bulbs, or tubers.
Term
Perfect flowers
Definition
Bisexual flowers. Includes stamens and carpels.
Term
Perforation
Definition
Areas lacking primary and secondary walls. Found on the perforation plates of vessel elements.
Term
Perforation plate
Definition
Areas on vessel elements with perforations. Aligned end to end to form the vessel.
Term
Perianth (angiosperms)
Definition
The calyx and corolla of a flower.
Term
Perianth (liverworts)
Definition
A tubular sheath which surrounds the archegonia of leafy liverworts.
Term
Pericarp
Definition

Ovary wall

May develop into the fruit. Thickens and becomes differentiated into layers: exocarp, mesocarp, and endocarp. The seed coat in grass seeds.

Term
Periclinal divisions
Definition
Cell plates form parallel to the surface of the meristem.
Term
Pericycle
Definition
Nonvascular cells surrounding vascular tissues in the vascular cylinder. Originates from the procambium. Lateral roots arise from the pericycle. Contributes to vascular cambium, and generally gives rise to the first cork cambium.
Term
Periderm
Definition

"Protective covering"

A dermal tissue. Covers plant parts that undergo secondary growth. Replaces epidermis. Cells are arranged compactly, but has lenticels to provide aeration of internal tissues. Consists of cork cambium, cork, and phelloderm. A new periderm is added each year in temperate plants.

Term
Perigynous flowers
Definition
The perianthe and stamens are adnate to the calyx, forming the hypanthium.
Term
Peripheral zone
Definition

Peripheral meristem

A component of the shoot apical meristem. Surrounds the central zone in a ring. Mitotically very active. The procambium and some parts of the ground meristem originate from the peripheral zone.

Term
Perisperm
Definition
Food storage tissue in the seed formed from the nucellus.
Term
Peristome
Definition
A ring of teeth surrounding the opening of the capsule of true mosses. Curls open when the air is dry, releasing spores. True mosses species differ in peristome structure.
Term
Peroxisome
Definition
A component of the cytoplasm. A single-membrane bound organelle 0.5 - 1.5 μm in diameter. A granular interior, may contain a body, sometimes crystalline, of protein. Closely associated with the ER, mitochondria, and chloroplasts. Self-replicating by fission, but possesses neither DNA nor ribosomes; imports all materials from the cytoplasm. Has movement within the cell. Plays a role in photorespiration. Freely transforms into a glyoxisome.
Term
Petal
Definition
A sterile flower part. Leaf-like in structure. Commonly bright coloured, and relatively thin. Collectively, they form the corolla. For petal formation in the ABCDE model, class A, B, and E function are needed.
Term
Petiole
Definition
The stalk-like portion which attaches the leaf to the node.
Term
Petrified wood
Definition
Trees become water-logged, sink, and volcanic ash replaces cells with quartz, creating petrified wood.
Term
Petunia hybridia
Definition
A model organism.
Term
Phagocyte
Definition

"Eating cell"

Capable of endocytosis: engulfing large particles including other bacterai, forming vesicles. Lacks a cell wall, flexible membranes, and a cytoskeleton. In the endosymbiotic theory, a heterotrophic prokaryotic cell lost its cell wall and became a primitive phagocyte.

Term
Phelloderm
Definition
A tissue of the periderm. Living parenchyma-like tissue. Arises from the inner surface of the cork cambium. Lacks suberin.
Term
Phenolic compounds
Definition
Found in peat moss. Has antiseptic properties, making peat moss good to use as dressing for wounds.
Term
Phenotype
Definition
The appearance of an organism.
Term
Phloem
Definition
A vascular tissue. The "super-information highway". Conducts sugars, amino acids, lipids, micronutrients, hormones (florigen), proteins, RNAs, and viruses throughout the plant. Primary phloem cells may be stretched and destroyed. Cells are sieve elements, connected at sieve areas. It is blocked with callose if damaged.
Term
Photodormancy
Definition
Dormancy where light quality and quantity triggers germination.
Term
Photomorphogenesis
Definition
When light has an effect on plant growth and development. Light may stimulate or inhibit growth. Light affects synthesis of chlorophyll.
Term
Photoperiodism
Definition
Discovered in the 1920s by W.W. Garner and H.A. Allard. Plants that only flower, or seeds that only germinate under certain day lengths. Allows organisms to detect the time of year and undergo seasonal developmental changes. Circadian clock provides a key feature of the timing of photoperiodism. Also found in some animals. Includes short-day, long-day, and day-neutral plants. Some plants require a single exposure to the correct day length, and some require several weeks of exposure. Temperature and maturity level can also affect flowering. Karl C. Hamner and James Bonner found that periodism is sensed in the leaf blade, plants measure the length of darkness, and that plants are most sensitive to red light at about 660 nm wavelength. The Beltsville group found that red light induces lettuce seeds to germinate, but far-red light inhibits it (it doesn't matter what order flashes come in, just the last flash matters).
Term
Photosynthesis
Definition

The process by which most autotrophs create organic molecules from sunlight. Chloroplasts perform photosynthesis in some eukaryotes.

6 O2 + 6 H2O → C6H12O6 + O2

Term
Phototropism
Definition
Troipsm in response to light. Parts that grow towards light have positive tropism. Parts that grow away from light have negative tropism.
Term
Phragmoplast
Definition
Barrel-shaped microtubule systems that form between two daughter nuclei during cytokinesis. Contains actin filaments prallel with the microtubules. Helps the Golgi apparatus from the cell plate.
Term
Phragosome
Definition
The plane in which plant cells divide. Forms in G1 phase from cytoplasmic strands that anchor the nucleus within the tonoplast.
Term
Phyllotaxis
Definition

Phyllotaxy

The arrangement of leaves on the stem. Includes spiral, distichous, opposite, decussate, and whorled. Explanations for phyllotaxis include first available space, inhibitory field hypothesis, biophysical forces, and the auxin-based model.

Term
Pylogenetic tree
Definition
A depiction of the phylogeny of a group.
Term
Phylogeny
Definition
The evolutionary history of an organism.
Term
Phylum
Definition

Plural, phyla

The category below kingdom and above class.

Term
Physcomitrella patens
Definition
A model plant bryophyte. Its genome is sequenced. One of the few known multicellular organisms with highly efficeint homologous recombination; enables scientists to perform gene replacement. Used in "moss bioreactors" which are used to produce valuable biopharmaceuticals.
Term
Phytochrome
Definition
A photoreceptor that senses light quality.
Term
Phytomere
Definition
Produced by the shoot apical meristem. A leaf, node, internode, and axillary bud.
Term
Pinnate
Definition
A type of compound leaf. Leaflets arise from the rachis.
Term
Pistil
Definition
Several fused carpels.
Term
Pit
Definition
Thin areas in the secondary wall. Permeable to water. Often occurs adjacent to pits on neighboring cells: pit-pairs. Includes simple pits and bordered pits. Occurs in tracheary elements of the xylem.
Term
Pit cavity
Definition
The cavity below the over-arching secondary wall in bordered pit.
Term
Pit membrane
Definition
The middle lemella between two opposite pits.
Term
Pit-pairs
Definition
Two pits on neighboring cells, adjacent to one another, and their pit membrane.
Term
Pitcher plant
Definition
A carnivorous plant. Insects fall into the sac and are digested.
Term
Pith
Definition
Parenchyma cells between the vascular bundles in the stem.
Term
Pith meristem
Definition
A region of the shoot apical meristem. Beneath the central zone. Some parts of the ground meristem originate from the pith meristem.
Term
Pith rays
Definition
Extra wide interfascicular regions.
Term
Placenta (angiosperm)
Definition
The portion of the ovary where ovules originate, and to which they remain attached until maturity. May be lobed, providing more surface area for ovule formation.
Term
Placenta (bryophyte)
Definition
Part of the sporophyte of bryophytes. It is the interface between gemetophyte and sporophyte, where matrotrophy passes between them. It is highly folded to increase surface area.
Term
Placentation
Definition
The arrangement of placentae within the ovary. Includes parietal, axile, free central, basal, and apical.
Term
Plantae
Definition
A kingdom within Eukarya. Contains plants. There are ten phyla within Plantae. Three are nonvascular (the bryophytes): Bryophyta, Marchantiophyta, and Anthocerotophyta. Two are vascular and seedless: Lycopodiophyta and Moliophyta. Five are vascular and seed-producing: Coniferophyta, Ginkgophyta, Anthophyta, and Cycadophyta.
Term
Plasma membrane
Definition
The outer boundary of the cytoplasm. Separates the protoplast from the external environment. Mediates transport of substances, co-ordinates synthesis of assembly of cell wall microfibrils. Detects and facilitates responses to hormonal and environmental signals.
Term
Plasmodesmata
Definition

Singular, plasmodesma

Narrow plasma-lined channels 30 - 60 nm in diameter. Occur throughout the cell wall, aggregated in primary pit fields and/or pit-pairs. Transversed by the desmotubule. Formed during cell division when the ER is trapped in the cell plate, but can form between non-dividing cells. Provide a pathway for substances between cells: sugars, amino acids, signaling molecules. Their existence was confirmed when the electron microscope was invented.

Term
Plasmogamy
Definition
The fusion of two zoospores.
Term
Plastid
Definition
A component of the cytoplasm. Has to membranes. May have its own ribosomes, which are two thirds of the size of cytoplasmic ribosomes. Have thylakoids in stroma. Includes chloroplasts, chromoplasts, leucoplasts, protoplasts, and etioplasts. May switch between certain types in response to the environment. Reproduce by binary fission, similar to a bacterium.
Term
Plumule
Definition
The embryonic shoot. Includes the epicotyl and young leaves.
Term
Polar microtubules
Definition
Spindle fibres not attached to kinetochores. Some are long enough to overlap with spindle fibres from oppsite end.
Term
Polar nuclei
Definition
Two of the nuclei in the embryo sac. In the centre of the embryo sac; found in the central cell.
Term
Polarity
Definition
One end is different from the other. Established with the asymmetric division of embryogenesis. In some species it is established in the egg cell and zygote: the nucleus is near one end, and tonoplast to the other.
Term
Pollen beetle
Definition
A possible pollinator. Attracted by floral scent.
Term
Pollen grain (angiosperm)
Definition
Consists of a pollen coat (exine and intine) vegetative cell, and generative cell. Dehisced from the anther in two-celled or three-celled stage. Can be from 10 - 350 μm in diameter, spherical or rod-shaped. Apertures may be long and grooved, round and porous, or a combination. Plants can often be identified solely by pollen structure. Pollen is well represented in the fossil record, providing insights into the kinds of plants that lived in the past.
Term
Pollen grain (gymnosperms)
Definition
It consists of two prothallial cells, a generative cell, and a tube cell. It is carried by the wind or fire to an ovule, where it lands on the pollination drop. After it penetrates the nucellus, the sterile cell and spermatogenous cell form.
Term
Pollen sac
Definition

Microsporangia

There are four pollen sacs in one another.

Term
Pollen tube
Definition
A tube that germinates from the pollen grain. At this point, gymnosperm megaspores begin to develop.
Term
Pollination
Definition
In gymnosperms, wind carries pollen to ovules. In angiosperms, a vareity of method may transfer pollen to the stigma (including animals). The pollen grain takes up water and germinates a pollen tube which grows through transmitting tissue, and is guided by chemiattractants. If pollen was released at two-celled stage, three-celled stage begins at this point. Angiosperm tube cells grow 1000 times faster than gymnosperms'. The pollen tube wall is reinforced with callose, giving tensile strength. Deposits callose plugs that seal off older portions of the tube as it grows, allowing for greater distance. Double fertilization occurs when it reaches the synergids.
Term
Pollination drops (PDs)
Definition
A drop of fluid found at the micropyle of gymnosperm ovules. Consists of water, sugars, amino acids, and organic acids; it functions in pathogen defense, and pollen development. Carries the pollen grain through the micropylar canal to the nucellus.
Term
Pollinium
Definition
The anthers of an Orchidaceae flower.
Term
Polygonum type
Definition
A type of megagametogenesis, occurs in 70% of angiosperms. Three of the four megaspores disintigrate, and the one farthest from the micropyle survives. Three mitotic divisions produce an eight-nucleate cell: the embryo sac. Triple fusion between teh sperm nucleus and polar nuclei form the primary endosperm nucleus.
Term
Polynomials
Definition
Twelver words used to describe each species. Used in Cal Linneaus's Species Plantarum.
Term
Polyphyletic group
Definition
A group that doesn't include the common ancestor of all members.
Term
Polyploid
Definition

"Multiple sets"

Cells with more than two sets of chromosomes.

Term
Polysomes
Definition
Clusters of ribosomes. May attach to the rough ER or the nuclear envelope.
Term
Polytrichum
Definition
A true moss where simple sugars transfer from gametophyte to sporophyte.
Term
Pome
Definition
A fleshy simple fruit. Develops from a compound inferior ovary. Most of the flesh is from the floral tube, and the endocarp enclosing the seed is cartilaginous. Example: apple, pear, quince.
Term
Pores
Definition
Small holes on the upper surface of bryophytes that increase CO2 permeability and reduce water loss. Similar to stomata found on vascular plants.
Term
Positional information
Definition
Plants communicate information on their fimal position in the cell, determining how it will differentiate.
Term
Preprophase band
Definition
A narrow band of microtubules just beneath the plasma membranee in a ring around the equator of the cell. Forms in G2 phase. Actin filaments align parallel to the preprophase band. It disappears before initiation of the cell plate, but the cell plate fuses where the preprophase band was. It is still present during prophase.
Term
Prickle
Definition
A defense adaptation. An outgrowth of the cortex and epidermis. The "thorns" on roses are actually prickles.
Term
Primary cell wall
Definition
A region of the cell wall, on the very exterior of the cell wall. Contains pectin, cellulose, hemicellulose, water, sometimes lignin, suberin or cutin, and proteins (glycoproteins, enzymes including peroxidases, phosphatases, cellulases, and pectinases). Has primary pit-fields. Formed while the cell is growing. The only cell wall layer in actively dividing cells, and cells involved with photosynthesis, respiration, secretion, or wound healing.
Term
Primary dormancy
Definition
Dormancy acquired during seed maturation.
Term
Primary endosperm nucleus
Definition
The triploid nucleus formed from triple fusion of the sperm cell with the polar nuclei. Develops into the endosperm.
Term
Primary endosymbiosis
Definition
Cells are engulfed and not digested and eventually form primary plastids. There are two membranes. Found in red algae, green algae, and glaucophytes. Primary plastids may have emerged more than once.
Term
Primary growth
Definition
Growth in the apical meristem. Extends the plant body. Forms the primary plant body.
Term
Primary meristems
Definition
Primary meristematic tissues. Appears in the embryo proper during embryogenesis. Protoderm, ground meristem, and procambium.
Term
Primary phloem fibres
Definition
Develop in the phloem after elongation of the internode is complete.
Term
Primary pit-fields
Definition
Thin areas in the primary cell wall. Plasmodesmata cluster in these areas.
Term
Primary plant body
Definition
The plant body which is formed by primary growth of the apical meristem.
Term
Primary root
Definition
The first structure to emerge from the seed. Originates from the embryo. It continues to grow, and develops lateral roots. In some monocots it dies, and adventitiousroots form. In all plants except monocots, it is called the taproot.
Term
Principle of parsimony
Definition
Cladograms should be constructed in the simplest, most efficient way.
Term
Procambial strands
Definition
Procambium which extends upwards into leaf primordia.
Term
Procambium
Definition
A primary meristem. Precursor of vascular tissue: xylem and phloem. Originates from the peripheral zone of the shoot apical meristem.
Term
Proembryo
Definition
The first stage of embryogenesis. The apical cell is towards the chalazal end. The basal cell is towards the micropylar end. Develops into the embryo proper.
Term
Programmed cell death
Definition
Genetically determined process that leads to the cell's death, precedes by mitochondrial swelling and release of cytochrome C, activating proteases and nucleases that degrade the protoplast. Occurs in tracheary elements, resulting in elimination of the protoplast, leaving only cell walls.
Term
Prokaryote
Definition
The first cells that existed. Simple, lacking nuclear envelope, absence of organelles, genetic material not organized into complex chromosomes.
Term
Prolamellar body
Definition
A semi-crystalline body composed of tubular membranes. Found in etioplasts. It becomes a thylakoid if the etioplast is exposed to light.
Term
Promeristem
Definition
The part of the root apicla meristem closest to the tip, and least differentiated. Composed of initials and immediate derivatives, with dense cytoplasm and large nuclei.
Term
Prop roots
Definition
Aerial roots that serve to support the plant. When they reach the soil, they branch and absorb water and minerals. Example: maize.
Term
Prophase
Definition
The first stage of mitosis. Th elongest phase in mitosis. Transition from G2 to prophase is not clearly defined. Chromatin condenses into chromosomes. The prophase spindle forms. The preprophase band is still present. The nucleolus disappears. Prophase ends when the nuclear envelop breaks down.
Term
Prophase I
Definition
The first stage of meiosis I. The chromosomes become visible, and shorten and thicken. Synapsis of homologous chromosomes, forming bivalents. The cores of homologs form a synaptonemal complex, and chromatids have crossing over at chasmata. The nuclear envelop breaks down. Homologous chromosomes repulse one another, but chromatids are held together at chiasmata.
Term
Prophase II
Definition
The first stage of meiosis II. The nuclear envelope disappears.
Term
Prophase spindle
Definition
Microtubules aligned parallel to the nuclear surface along the spindle axis. Forms in prophase.
Term
Protective layer
Definition

Leaf scar

A layer in the abscission zone. A stronger layer of cells, isolates the separation layer from the stem. Visible on the stem after the leaf forms.

Term
Proteinases
Definition
An enzyme released in the seed that digests stored starches.
Term
Prothalial cell
Definition
One of the cells in a gymnosperm pollen grain.
Term
Prothallus
Definition
The gametophyte of ferns. It is a small, green, heart-shaped, haploid structure with rhizoids that provide anchorage. It is photosyntehtic if it is above the ground, and if it is underground, it forms a symbiotic relationship with fungi for nutrition. May be bisexual or unisexual. Free water is required for fertilization; carries sperm from an antheridia to an archegonia. The sporophyte grows out of the archegonia after fertilization.
Term
Protoderm
Definition
A primary meristem. The precursor of the epidermis. Formed by periclinal divisions in the outermost cells of the embryo proper.
Term
Protofilament
Definition
Composed of tubulin subunits. 13 arrange to form a microtubule.
Term
Protonema
Definition

"First thread"

The young gametophyte which germinates from the spore of a bryophyte. Found in all mosses, some liverworts, but not hornworts.

Term
Protophloem sieve tubes
Definition
First-formed primary phloem elements. Reach maturity nearer to the root tip than protoxylem elements; nutrients need to be transported for root growth.
Term
Protoplasm
Definition
The contents of the plant cell. Includes the cytoplasm and plasma membrane.
Term
Protoplast (cell)
Definition
Derived from the protoplasm. The unit of the protoplasm inside the cell wall.
Term
Protoplast (plastid)
Definition
A plastid. Small, colourless or pale green, undifferentiated plastids. Can differentiate into chloroplasts, chromoplast, or leucoplasts. If it is not exposed to light, it may become an etioplast. Occur in meristematic cells.
Term
Protoxylem elements
Definition
First-formed primary xylem elements.
Term
Protoxylem lacuna
Definition
A space that forms as the protophloem and protoxylem are stretched and destroyed during internodal elongation.
Term
Protoxylem poles
Definition
Tips of the ridges of primary xylem in a root.
Term
Protracheophyte
Definition
A fossil plant, an intermediate between bryophytes and tracheophytes. Had hadrom and leptom.
Term
Pseudoelaters
Definition
Structures between the spores in the sporophyte of Anthoceros, that twist as the sporophyte dies, dehiscing spores.
Term
Pseudopodium
Definition
The stalk which holds up the sporophyte of sphagnum moss. Part of the gametophyte. Can reach up to 3 mm long.
Term
Psilotophyta
Definition

Whiskferns

A member of pterophyte. A phyla of seedless vascular plants. Dominated in the Late Devonian period through to the Carboniferous Period.

Term
Pteriodopyta
Definition
A member of pterophytes.
Term
Pterophytes
Definition

Monilophyta

Vascular, seedless plants. Includes whisk ferns, horsetails, and ferns.

Term
Punnett square
Definition
A diagram showing all possible offspring results from a cross. Named after the English geneticist who first used it.
Term
Puya raimondii
Definition
A relative of the pineapple which can reach 10 m high. Found in the Andes. Takes about 150 years to flower.
Term
Pyrenoid
Definition
A large plastid which produces and stores food.
Term
Quercus suber
Definition

Cork oak

Produces commercial cork. Native to the Mediterranean. After 20 years, the tree begins to produce cork. It takes 10 years for the cork layer to become thick enough to harvest.

Term
Quiescence
Definition

"Resting"

The embryo has halted growth and will germinate when conditions are favourable.

Term
Quiescent centre
Definition
A relatively inactive region in the root apical meristem, corresponding to the promeristem. Doesn't include the initials of the root cap. Has the ability to repopulate bordering meristematic regions when they are injured. Plays an essential role in the development of the root. Most cell divisions occur close to the quiescent centre.
Term
Quillworts
Definition

Lycopodiophyta

A member of lycophytes. Now extinct.

Term
Rachis
Definition
An extension of the petiole, from which leaflets of a pinnate compound leaf arise.
Term
Radical pattern
Definition
A pattern established in embryo genesis. Pattern about the main axis.
Term
Radially symmetrical flowers
Definition

Regular flowers

Actinomorphic, "ray". The different whorls are made of members of similar shape that radiate from the centre of the flower. Example: rose, tulips.

Term
Radicle
Definition
The embryonic root. Attaches to the hypocotyl at the hypocotyl-root axis.
Term
Ray
Definition
Horizontal lines of parenchyma cells in secondary vascular tissues.
Term
Ray cells
Definition
Produced by the ray initials of the vascular cambium. Form vascular rays. Composed mostly of variable length parenchyma. Store starch, proteins,and lipids, and many synthesize some metabolites.
Term
Ray flowers
Definition
Flowers on the periphery of the composite head of Asteraceae flowers. Mostly sterile, but some are carpellate. In some the corolla is fused  to form a single strap-like "petal".
Term
Ray initials
Definition
A component of the vascular cambium. Horizontally oriented, square cells. Produce ray cells.
Term
rbcL
Definition
The gene that encodes for the large subunit of rubisco. Present in all photosynthetic eukaryotes and cyanobacteria. Has no introns. Useful in studying relationships between plants. A barcode for pants, but can be supplemented with additional markers as required. Works better for some plants than others.
Term
Reaction wood
Definition
Development responses to leaning branches or stems, to counteract the force of gravity. Increased activity of the vascular cambium, resulting in wider growth rings.
Term
Receptacle
Definition
The part of the flower stalk to which flower parts are attached.
Term
Recessive allele
Definition
Expressed only in homozygous individuals.
Term
Region of elongation
Definition
The region behind the root apical meristem. A few milimeters in length. Elongation of cells increases the length of the root. Above this region the root length does not increase.
Term
Region of maturation
Definition

Region of differentiation

Root-hair zone

The region behind the region of elontation. Cells of most primary tissues mature. Root hairs are produced.

Term
Resin ducts
Definition
Large intercellular spaces lined with thin-walled parenchyma in softwoods. A product of trauma. Secrete resins, which defend against fungus and insects.
Term
Respiration
Definition
A more efficientway to utilize oxygen in heterotrophs. Aerobic breakdown of energy rich, complex compounds, more efficient than anaerobic processes. Arose 700 million years ago when oxygen levels went up due to autotrophs. Mitochondria perform respiration in eukaryotes.
Term
Resting stage
Definition
One of the forms of non-dispersive P protein bodies. Condensed.
Term
Rhizoids
Definition
Small anchors on the lower surface of bryophytes, and the protahllus of ferns that anchors them to and allows them to feeds on their substrate. In liverworts and hornworts they are unicellular.
Term
Rhizomes
Definition
Long, thin, underground stems. Arise from cutting-planted potatoes.
Term
Rhizosphere
Definition
The soil around living plant  roots. Roots excrete substances into the rhizosphere.
Term
Rhyniophyta
Definition
An extinct phyla of seedless vascular plants. Went extinct by the Devonian period, 360 million years ago.
Term
Ribosomes
Definition
Components of the cytoplasm. Small particles 17 - 23 nm in diameter, consisting of protein and rRNA that is produced in the nucleolus. Consists of the small and large subunits which are produced separately. The site at which amino acids link together to form proteins. Found free in the cytosol or attached to the ER, plasmids, and/or mitochondria. May occur in clusters of polysomes. All ribosomes in a particular organism are identical.
Term
Riccia
Definition
A group of complex thalloid liveworts. One of the simplest lverworts. The main and subsequent axes fork into two branches. The sporophyte is simply a spherical capsule. Some species are aquatic. Some are unisexual, some bisexual.
Term
Ricciocarpus
Definition
A group of complex thalloid hornworts. Bisexual.
Term
Ring-porous wood
Definition
Woods where early wood has larger vessels than late wood. Water is conducted much faster in teh outermost layer of growth.
Term
Root
Definition
Underground portion of the plant. Function in anchorage, absorptioin, storage,conduction, clonal regeneration, production of hormones and secondary metabolites, and excretion of substances into the rhizosphere.
Term
Root apical meristem (RAM)
Definition

Region of cell division

The apical meristem in the tips of roots. Give rise to roots. Has closed or open apical organization. The region of actively dividing cells in the root apical meristem. Behind the promeristem. Length differs with species and root development.

Term
Root cap
Definition
A mass of living parenchyma cells that protects the root acpical meristem, and aids it through the soil. Senses, processes, and transmits signals to the meristem and elongation region of the root, controlling the direction of root growth. Includes border cells, columella, and the lateral root cap.
Term
Root hair
Definition
Trichomes that facilitate the uptake of water and minerals by roots. Greatly increases absorptive surface. There are about 14 billion in one rye plant, amounting to 400 m2 of surface area. Short-lived and confined to the region of maturation. New root hairs are produced behind of cell elongation.
Term
Root primordium
Definition

Young lateral root

It pushes through the cortex as it increases in size, perhaps secreting enzymes to digest the cortex. Develops a root cap and apical meristem. The vascular cylinders of the lateral root and parent root are joined when derivatives of intervening pericyle and vascular parenchyma cells differentiate into xylem and phloem.

Term
Root-shoot junction
Definition
The region where the root and shoot system connect. Near the surface of the soil.
Term
Rough ER
Definition
A region of the ER. Consists of cisternae with numerous polysomes on the outer surface. Involved in protein synthesis. May be continuous with the nuclear envelope in some places.
Term
Rubber
Definition
99% of the world's rubber comes from Thailand. The plant is killed by a fungus if you try to grow it in North or South America.
Term
Rubisco
Definition
The most abundant protein on earth. Present inall photosynthetic organisms. The gene for this protein is used to analyze the relationship between large plant groups.
Term
S phase
Definition

Synthesis phase

The second phase of interphase. A key phase for DNA replication.

Term
Samara
Definition
A winged achene. Example: ash, elm.
Term
Sapwood
Definition
Younger, conducting wood with livign cells and reserve  materials. Often lighter in colour.
Term
Scarification
Definition
Abrasion that breaks the seed coat or removes growth inhibitors. Done with a knife, file, or sandpaper.
Term
Schizocarp
Definition
An indehiscent, dry simple fruit. Characteristic of the parsely and maple families, and some other groups. Splits at maturity into two or more one-seeded portions.
Term
Sclereid
Definition
A type of sclerenchyma cell. Variable in shape, often branched. Relatively short compared to fibres. May occur singly or in aggregates throughout ground tissues. Make up the seed coat of seeds, the shells of nuts, and the endocarp of stone fruits. Give the "gritty" texture to pears.
Term
Sclerenchyma cells
Definition
The constituents of sclerenchyma tissue. Very thick cell wall, 90% of cell volume. Often lack protoplast and are dead at maturity. Occur in small groups, or individually among other cells. Includes fibres and sclereids.
Term
Sclerenchyma tissue
Definition
A ground tissue. Continuous masses. Consists of sclerenchyma cells. Develop in parts of the primary and secondary plant body. Thick, often lignified secondary walls. Strengthen tissues that have ceased elongating.
Term
Scutellum
Definition
The cotyledon in grass seeds. Attahced to one side of the axis of the embryo.
Term
Second four-nucleate stage
Definition
The second stage in fritillaria type megagametogenesis. The nucleus at the micropylar end divides to form two nuclei. The three nuclei at the chalazal end come together to form a triploid nucleus, and then divides to form two triploid nuclei.
Term
Second node
Definition
The node where the first true leaves are attached to the stem. In grasses the coleoptile attaches to this node.
Term
Seconday cell wall
Definition
A region of the cell wall. Additional cell wall layers laid down by the protoplast on the inner surface of the primary wall. Found in many cells, but not all. Deposited after the cell has finished growing. Important in cells with structural function, especially cells that are dead at maturity (xylem). Contains cellulose, hemicellulose, lignin. There may be no pectins, and proteins are absent. There are three layers (S1, S2, and S3), which differ in orientation of microfibrils. Stronger than the primary wall. Has pits.
Term
Secondary dormancy
Definition
Dormancy due to unfavourable conditions after primary dormancy has passed.
Term
Secondary endosymbiosis
Definition
A eukaryotic cell with plastids is itself engulfed by a eukaryotic cell, forming a secondary plastid. There are three or four membranes. Found in haptophytes, most cryotmonads, and many euglenoids, dinoflagellates, adn stamenopiles.
Term
Secondary growth
Definition
Growth in the lateral meristem. Thickens the stems and roots.
Term
Sedges
Definition

Cyperaceae

Resemble grasses. Flowers have no petals, no sepals, 3 stamens, and 1 carpel. The "spikelet" flowers are incomplete, but perfect.

Term
Seed
Definition
A plant embryo surrounded by stored food and a seed coat. A dramatic innovation in the evolution of vascular plants. Increases survival.
Term
Seed bank
Definition
Preserves of genetic characteristics of wild and early cultivated varieties of crop plants for use in future breeding programs. Protects dwindling genetic diversity.
Term
Seed coat
Definition

Testa

The outer coat of the seed. Develops from integuments. Protects the embryo and endosperm. Thinner than the integuments. May be thin, dry, and papery, or very hard and impermeable to water.

Term
Seed-scale complex
Definition
A component of a megasporangiate. Consits of of an ovuliferous scale with an ovule on top, and a sterile bract below. The megaspore mother cell is surrounded by the nucellus.
Term
Seed vascular plants
Definition
Includes gymnosperms and angiosperms. All plants except ferns and bryophytes.
Term
Seedless vascular plants
Definition
Includes lycopodiophyta and pteridophyta.
Term
Selaginella
Definition
A seedless vascular plant. The suspensors function to push the developing embryo into nutritive tissues.
Term
Self-incompatibility
Definition
A genetic mechanism that prevents self-fertilization. Promotes outcrossing, generating new genotypes. One of the causes of the success of angiosperms. The pollen grain may not fit on the stigma, may be prevented from germinating, destroyed by enzymes as they enter the pollen tube, or the zygote may not develop.
Term
Seminal root
Definition
Roots that separate from the axis formed by the plumule and cotyledon.
Term
Sepal
Definition
A sterile flower part. Leaf-like in structure. Below the petals. Commonly green and relatively thick. Collectively, they form the calyx. For sepal formation in the ABCDE model, class A and E function are needed.
Term
Separation layer
Definition
A layer in the abscission zone. Relatively short cells with poorly developed wall thickenings. Structurally weak. Cell walls are broken down by enzymes. This layer separates from the main branch as the parenchyma cells enlarge.
Term
Sessile leaf
Definition
A leaf with a petiole; attached directly to the stem. The base of the leaf expands into a sheath that surrounds the stem. Most common in monocots.
Term
Seta
Definition
A component of the sporophyte in bryophytes. A stalk that connects the capsule to the foot.
Term
Sexual deception
Definition
A tactic in flowers for attracting pollinators. Mimics the apperance of female insects, and releases scents similar to their pheromones.
Term
Sheath
Definition
The base of a sessile leaf, surrounding the stem. In some grasses, it extends the length of the internode.
Term
Shoot
Definition
The stem and leaves. The above-ground portion of the plant. Initiated by the plumule of the embryo. Structurally more complex than the root. Has nodes where leavs attach. Supports the leaves and conducts water and photosynthates to where they are needed.
Term
Shoot apex
Definition
The apical meristem and the subapical region bearing leaf primordia.
Term
Shoot apical meristem (SAM)
Definition
The apical meristem at the tip of shoots. Gives rise to stems, leaves, and flowers. In the embryo of eudicots, it is between the two cotyledons. In the embryo of monocots, it is to the side of the cotyledon, and covered by the coleoptile. Produces phytomeres. Lacks a protective structure analogous to the root cap, but often has young leaves that fold over it. Has tunica-corpus organization. Includes the central zone, peripheral zone, and pith meristem.
Term
Short-day plants
Definition

Long-night plants

Flower in early spring or fall. Need a light period shorter than a critical length. Example: cocklebur.

Term
Shuttle vesicle
Definition
Transports glycoproteins to subsequent cisternae in the Golgi body.
Term
Sieve
Definition
A cluster of pores through which adjacent sieve elements are interconnected.
Term
Sieve areas
Definition
Areas on sieve elements through which the protoplasts of adjacent sieve elements are connected by plasmodesmata. Blocked wtih callose if the phloem is damaged.
Term
Sieve cells
Definition
A sieve element. Occurs only in gymnosperms. Lacks sieve plates. Sieve area pores are narrow and uniform on all walls, concentrated on overlapping ends of sieve cells.
Term
Sieve element
Definition
The cells of phloem. Connected to each other at sieve areas. At maturity the nucleus, vacuole, ribosomes, Golgi apparatus, and cytoskeleton are lost. Living protoplasts, mitochondria, and ER are distrbuted along the walls. Live at maturity, undergoes selective breakdown. Includes sieve cells and sieve-tube elements.
Term
Sieve plate
Definition
An area on a sieve-tube element with larger pores. May occur on any wall, but generally on end walls.
Term
Sieve tube
Definition
A continuous column of sieve-tube elements arranged end-to-end.
Term
Sieve-tube elements
Definition
A sieve element. Occurs only in angiosperms. Arranged end-to-end to form the sieve tube. Sieve area pores differ in size in the same cell. Has sieve plates. Cloesly associated with companion cells, which keep it alive.
Term
Silique
Definition
A dehiscent, dry simple fruit. Characteristic to the mustard family. Forms from two carpels. The two halves split at maturity, leaving a persistent central partition to which seeds are attached.
Term
Simple fruit
Definition
A type of fruit. Develop from a single carpel, or from two or more united carpels. Example: bean, cherry, tomato. Fleshy simple fruits include berries, drupes, and pomes. Dry simple fruits include dehiscent and indehiscent fruits.
Term
Simple leaf
Definition
A leaf with a single, undivided blade. With or without a petiole and leaf sheath.
Term
Simple pits
Definition
Pits with no over-arching.
Term
Simple thalloid liverworts
Definition
A type of liverwort. Ribbons of undifferentiated tissue.
Term
Siphonous marine algae
Definition

Green algae

A group of Ulvophyceae. Have multinucleate tubular cells that are large, branched, and rararely sepate, with a large central vacuole. Develop without the formation of cell walls. Some cells are as long as a meter. Have gametic meiosis. Includes Codium.

Term
Simple tissues
Definition
Tissues composed of one type of cell. Includes ground tissues.
Term
Sister chromatids
Definition
Identical chromatids which are connected at the centromere to form a chromosome.
Term
Sister groups
Definition

Closest relatives

Groups terminating in adjacent branches on a cladogram.

Term
Slime plug
Definition
An accumulation of P protein that blocks a sieve tube element to prevent loss of water and food substances.
Term
Smooth ER
Definition
A region of the ER. Lacks ribosomes; largely tubular, involved in lipid synthesis.
Term
Snow algae
Definition
Chlorophytes that live in snow. Can be red or green.
Term
Softwood
Definition
Wood from conifers. Lacks vessels, and has small amounts of parenchyma. The dominant cell type is tracheids, which have tori in their pit membranes. Average of 8% of the wood volume is rays. Parenchyma are found in resin ducts.
Term
Sori
Definition

Plural, sorus

Orange, brown, or black clumps found on the underside of fern fronds. The pattern that sori make are distinctive for each species. Some sorie have indusium. Contains numerous sporangia. Produces spores which are dispersed by the annulus.

Term
Spadix
Definition
A type of inflorescence having small flowers on a fleshy stem surrounded by a spathe. Near the bottom of the spadix, inside the spathe there are two rings of small flowers: the upper ring is staminate, and the lower ring is carpellate. Example: Amorphophallus titanum.
Term
Spathe
Definition
A single large sheath-shaped petal which surrounds the flowers of a spadix inflorescence.
Term
Species
Definition
The category below genus.
Term
Species Plantarum
Definition

"The Kinds of Plants"

A book published in 1753 by Carl Linneaus. Used polynomial names to describe plants.

Term
Specific epithet
Definition
The second term in a binomial system. May not be written by itself, since multiple species from different genera may have the same specific epithet.
Term
Specific gravity
Definition
The ratio of the substance to the weight of an equal volume of water. For wood, this is measured by the oven-dry weight of the wood.
Term
Sperm
Definition

The male gamete.

In bryophytes, they must swim through water to reach the egg, attracted by chemical attractants.

Iin gymnosperms, two arise from the spermatogenous cell in the pollengrain.

In angiosperms they form from the generative cell in three-celled stage of microgametogenesis.

Term
Spermatogenous cell
Definition
One of the two cells which form in a gymnosperm pollen grain after it penetrates the nucellus. It forms two sperm cells which are discharged into the ovary.
Term
Spermatogenous tissue
Definition
A component of an antheridia. Produces sperm.
Term
Spermatophytes
Definition
Vascular, seed plants. Includes gymnosperms and angiosperms.
Term
Sphagnidae
Definition

Peat moss

A class of moss. The protonema have peculiar morphology: a one-cell thick plate that grows by a marginal meristem. The gametophyte arises from a budlike structure from a marginal cell, then divides to form leaves and stem tissues. Spores are dispersed by the explosive operculum method. There are two genera: Sphagnum and Ambuchanania.

Term
Sphagnum
Definition

Peat moss

A genera of Sphagnidae. Diverged early in the evolution of moss. THe stems have five branches to a node, denser near the tip. Branches and stems have leaves, but stem leaves often lack chlorophyll. LEaves are one cell thick, made of hyaline cells each surrounded by narrow green or red cells with several disk-shaped chloroplasts. Cells contain decay-resistant phenolic compounds with antiseptic properties. Release hydrogen ions that lower the pH of their environment as low as 4.0. Can hold up to 20 times their dry weight in water. 

Gametangia are on the end of special branches. Fertilization takes place in the winter, and mature spores are released 4 months later. Sporophytes are blackish-brown, spherical capsules, held up by the pseudopodium. The operculum overs the capsule. As the capsule dries, it changes shape, increasing internal air pressure to 5 bars! The operculum is blown off, making a "click" sound, and the escaping gas blows spores out in an explosive burst. The average launch velocity is 16 m/s.

Reproduces asexuall by breaking stems off the gametophyte and regenerating a gametophyte.

Can be used as a diaper material, dressing for wounds, packing material for roots, as a soil additive, and as a fuel.

Peat mosses live in bogs that cover 1% - 3% of the Earth's surface. Peat moss contain large amounts of carbon. Harvest of peat moss is a multi-million dollar industry that is degrading wetlands in some areas.

Term
Spike moss
Definition

Sellaginella

A member of lycophytes. About 750 species. Huge range of environments: tropical to desert. Have microphylls. A model organism for lycophytes. The megasporangia and microsporangia are on the same strobili, so water is not needed for fertilization.

Term
Spindle assembly point
Definition
The checkpoint at the end of anaphase. Delays cell cycle if the chhromosomes are not properly attached to the mitotic spindle.
Term
Spindle fibres
Definition
Bundles of microtubules of differing lengths that form the mitotic spindle. The minus end is near the poles and the plus end is near the equatorial plate. Includes kinetochore and polar microtubules. Actin filaments form a "cage" around the spindle.
Term
Spine
Definition
A defense adaptation. A modified leaf. Originates on bud scales. The spines of bulls-horn acacia provide shelter for ants that kill other insects.
Term
Spiral
Definition

Helical

A phyllotaxis. The most common phyllotaxis. There is one leaf at each node, and the leavs form a spiral pattern around the stem. Example: oak, mulberry.

Term
Spirogyra
Definition

Related to desmids. An unbranched, filamentous, freshwater charophyte. Each filament is surrounded by a watery sheath. Helical arrangements of ribbon-like chloroplast in each uninucleat cell. There are no flagellate cells at any stage.

Reproduce aseuxally by cell fragmentation.

Reproduce sexually by conjucation tube that forms between two filaments. The zygote becomes surrounded by thick walls containing sporopollenin, enabling the zygote to survive harsh conditions for long periods, and germination when conditions improve.

Term
Spongy parenchyma
Definition
A type of cell of the mesophyll. Irregularly shaped, usually on the lower side of the leaf.
Term
Sporangia
Definition
Found in the sori of ferns. Produces spores.
Term
Sporangiophore
Definition
Structures that bear sporangia.
Term
Sporangium
Definition
A component of the sporophyte of bryophytes. Inside the capsule. Produces and releases spores.
Term
Sporic meiosis
Definition

An alternation of generations, found in plants, brown, red, and green algae (including Ulvophyceae), two genera of chytids, and some protists.

The diploid sporophyte produces haploid spores with meiosis. The spores divide to form haploid gametophytes that produce gametes that fuse to form zygotes that divide to form diploid sporophytes. 

Term
Spore
Definition

A cell that can develop into an organism without fertilization. Often it divides mitotically, producing multicellular organisms that are haploid.

The haploid, single-cellular stage of sporic meiosis. Arise from meiosis in the sporophyte. 

In bryophytes it germinates to form the protonema, which develops into the gametophyte. Bryophyte spores are coated in sporopollenin.

Term
Sporogenous cells
Definition
Celsl in the microsporangia that develop into microsporocytes. Four columns are found in the anthers. Nourished by the tapetum.
Term
Sporophyll
Definition
Produces spores in Lycophyta. Grouped into strobili. Heterosporous: unisexual gametes are produced.
Term
Sporophyte
Definition
Diploid, multi-cellular stage of sporic meiosis. Develop from the zygote. Undergo meiosis to produce spores. In bryophytes the sporophyte is small and nutritionally dependent on the parental gametophyte, consisting of a foot, a seta, and a capsule. In vascular plants the sporophyte is dominant: allows for increased number of spores produced per fertilization event.
Term
Sporopollenin
Definition
The most decay and chemical resistant biopolymer known. It is impregnated in the walls encasing bryophyte spores, pollen grains, and the zygote of Spirogyra and Chara. Enables organisms to survive in unfavourable conidtions. Composed of carotenoids, providing a strong barrier against UV radiation, dehydration, and pathogens.
Term
Stalk
Definition
A component of both anteridia and archegonia. Holds these organs aloft on both male and female bryophytes.
Term
Stamen
Definition
A reproductive flower part: pollen-bearing. Collectively, they form the androecium. Consists of the filament, anther, and pollen sacs. For stamen development in the ABCDE model, class B, C, and E function is needed.
Term
Staminate flowers
Definition
Imperfect flowers that have stamens.
Term
Stem
Definition
Provide support for leaves. Water moves upwards through the stems.
Term
Stem bundle
Definition
Vascular tissue from which a leaf trace extends. One stem bundle may have several leaf traces.
Term
Sterile bract
Definition
A component of a seed-scale complex. Below the ovuliferous scale.
Term
Sterile cell
Definition

Stalk cell

One of the cells which forms in a gymnosperm pollen grain after it penetrates the nucellus.

Term
Sterile jacket layer
Definition
A component of an antheridium. A sterile layer, one cell thick, that surrounds the spermatogenous cells.
Term
Stigma
Definition
Part of a carpel. The upper section, which receives pollen. Typically hairy or bumby, and may be wet. Often it is lobed. May be wet, dry, or open.
Term
Stilt roots
Definition
Roots produced from stems and branches. Often found in tropical trees.
Term
Stipule
Definition
A leaf-like, paired appendage on the stem, located on either side of the petiole base. Can occur near the basal part of a leaf, or nearly encircling the stem.
Term
STM
Definition

SHOOTMERISTEMLESS

The gene which establishes the shoot apical meristem in the embryo late in globular stage, first expressed in one or two cells. Loss of STM function causes seedlings with normal roots, hypocotyl, and cotyledons, but lakcing apical meristems.

Term
Stolons
Definition
Slender stems that grow along the surface of the ground. Arise from seed-planted potatoes.
Term
Stomata
Definition

Singular: stoma

A pore on the aerial parts of a plant, controlled by the guard cells and subsidiary cells. In dicots they are scattered on teh surface of the leaf. In monocots they are arranged in rows on the leaf. Occur on either side of a leaf, mostly on the underside. Allows for gas exchange.

Term
Stomatal complex
Definition
Guard cells, subsidiary cells, and stomata.
Term
Stomatal crypt
Definition
A depression in the leaves of xerophytes, where stomata and trichomes may be found.
Term
Storage
Definition
A function of roots. Substances move from the shoot into storage tissues in the roots. In biennials, large amounts are stored in the first year, enabling growth in the second year.
Term
Stratification
Definition
A long period of cold temperatures in order to stimulate germination in seeds. Moist seed is kept at 5ºC for 100 days. In nature this germination requirement is satisfied by winter.
Term
Streptopyte clade
Definition

Contains most charophycean orders: Coleochaetales, Charales, zygnemataleans, bryophytes, and vascular plants.

Mesostigma is at the base of the clade.

Term
Strobili (gymnosperms)
Definition

Cones

Includes the megasporangiate and microsporangiate. The microsporangiates are on lower branches than megasporantiates, to prevent self-fertilization.

Term
Strobili (spike moss)
Definition
Groups of sporophylls on Lycophyta densely aggregated along the stem.
Term
Stroma
Definition
A homogenous mixture in plastids. Thylakoids float in the stroma.
Term
Stroma thylakoid
Definition
Thylakoids which connect grana thylakoids in chloroplasts. Transverse the stroma.
Term
Stromalites
Definition
The oldest known organisms. Fossils found in Western Australia. Microbial mats of filamentous microorganisms trapped in sediment. They continue to form in places today, mostly warm shallow oceans of the shores of Australia and in the Bahamas.
Term
Structural support
Definition
An adaptation that was necessary for vascular plants. Lignified strengthening tissues to withstand gravity and maintain upright growth.
Term
Style
Definition
Part of the carpel. The middle section, through which pollen tubes grow. Absent in some species. With a pistil, there may be a common style.
Term
Suberin
Definition
A component of the cell wall. Found in secondary protective tissues: cork. Occurs in combination with waxes.
Term
Subsidiary cells
Definition
A type of epidermal cell. Differs in shape from guard cells, but plays a role in stomata control.
Term
Sudan III/IV
Definition
A stain which stains lipids orange/red.
Term
Superior flowers
Definition
The calyx, corolla, and androecium attach to the receptacle below the ovary.
Term
Suspensor
Definition
A stalk derived from the basal cell that anchors the embryo to the microphyle during embryogenesis. Metabolically active. Provides the embryo with nutrients and hormones, especially gibberellins. Connected to the embryo by plasmodesmata. May be one or many cells. Undergoes programmed cell death at torpedo stage.
Term
Svaldbard Gobal Seed Vault
Definition

Doomsday Vault

A vault on an island off the coast of Norway. Contains thousands of samples of seeds stored at - 18ºC in a dry chamber. Created in 2008. Stores duplicates of seed samples, preserves exotic sources of germplasm whcih may aid future breeding programs. Made by the Norwegian government. The vault was recently used to give seeds to Syria after the war.

Term
Symbiosis
Definition
A close association between two or more organisms that may be beneficial to each other.
Term
Symplastic pathway
Definition
Moving from one protoplast to another through plasmodesmata.
Term
Sympodium
Definition

Plural: sympodia

A stem bundle and its associated leaf traces. May be interconnected or independent.

Term
Synaptomorphy
Definition
Characteristics that arose in the common ancestor of a monophyletic group, and are present in all of its members. Used in cladistics to analyze phylogenies.
Term
Synapsis
Definition
Pairing of homologous chromosomes during prophase I, forming bivalents.
Term
Synaptonemal complex
Definition
The axial cores of homologous chromosomes, 0.1 μm apart during prophase I.
Term
Synergids
Definition
Two cells in the egg aparatus of the embryo sac at the micropylar end. Have thickened, convoluted cell walls. Release chemoattractants to attract sperm cells. Sperm cells are deposited into one of the synergids and they both desintegrate.
Term
Systematics
Definition
The sceintific study of biological diversity and its evolutionary history. The goal is to discovere all branches of the tree of life. Plant systematics is particularly focused on the generation of a database of sequences of the chloroplast gene rbcL, for rubisco.
Term
Tapetum
Definition
The innermost layer of the pollen sac. Nourishes sporogenous cells, produces orbicule proteins for pollen compatibility recognition, adds lipid-rich layers to the pollen grains, forms sporopollenin of the exine, and releases IAA, a developmental hormone. Secretes callase that digests the callose connecting pollen grains.
Term
Taproot
Definition
The primary root in all plants except monocots.
Term
Taproot system
Definition
Found in all plants except monocots. The taproot grows directly downward, giving rise to lateral roots. Reaches deeper than fibrous root systems.
Term
Taxol
Definition
A drug derived from a plant that is used to treat all types of cancer. A cell division inhibitor.
Term
Taxon
Definition

Plural: taxa

Taxonomic groups at any level.

Term
Taxonomy
Definition
Identifying, naming, and classifying species.
Term
Telophase
Definition
The fourth phase of mitosis. The nuclear envelop forms around the separated chromosomes, derived from the ER. The mitotic spindle disappears. Chromosomes decondense. Nuclei reform.
Term
Telophase I
Definition
The fourth stage of meiosis I. Chromosomes uncoil, and become indistinct. A nuclear envelop forms, the spindle disappears. In many organisms there is no interphase between meiosis I and II.
Term
Telophase II
Definition
The fourth stage of meiosis II. New nuclear envelops form, contracted chromosomes uncoil. Walls develop around each new cell.
Term
Tendril
Definition
A modification of the stem or leaf. Aids in support. Sometimes produces small leaves or flowers.
Term
Tension wood
Definition
Reaction wood found in angiosperms. Develops on the upper side of the leaning part. Has gelatinous fibre in a gelatinous layer.
Term
Tepal
Definition
When sepals and petals are very similar or indistinguishable. Often they are petal-like and showy.
Term
Tertiary endosymbiosis
Definition
A eukaryotic cell with secondary plastids is engulfed by a eukaryotic cell, forming tertiary plastids. There are more than two membranes. Found in several dinoflagellate species.
Term
Test cross
Definition
Crossing an individual with a homozygous recessive individual to determine the genotype.
Term
Thalli
Definition
Undifferentiated, thin, twig-like bodies which facilitate the uptake of CO2 and water in thalloid plants (liverworts and hornworts). There may be pores on the surface that optimize water loss and CO2 uptake.
Term
Thalloid
Definition

"Green shoot"

Has branched, flat gametophytes called thalli. Some liverworts and hornworts are thalloid.

Term
Thallus
Definition
Any type of body which is not differentiated into root, stem, or leaf.
Term
Thorn
Definition
A defense adaptation. A modified stem. Originates in the axils of leaves.
Term
Three-celled stage
Definition

Pollen mitosis II

The second stage of microsporogenesis. The generativel cell divides to form two sperm cells. Pollen is dehisced from the anther at this stage in some angiosperms. The sperm cells and vegetative nucleus form the male germ unit.

Term
Thylakoid
Definition
A system of flattened sacs inside a plastid. Float in stroma.
Term
Tissue
Definition
Organizations of cells forming structural and functional units.
Term
Tissue systems
Definition
Groups of tissues based on continuity in the plant. There are three primary tissues, all present in roots, stems, and leaves: ground, vascular, and dermal
Term
Tobacco
Definition
Nicotine is made in the roots and transported to the leaves. Nicotine is an insecticide.
Term
Tonoplast
Definition
A single, large vacuole in a plant cell. Develop from numerous small vacuoles that fuse together. Up to 90% of the cell volume may consists of the tonoplast: saves on "expensive" cytosol, and gives the cell turgor pressure strength. Filled with cell sap. Stores molecules. Sequesters toxic secondary metabolites, can contain anthocyanins. Break down macromolecules or entire organelles and recycle the components in the cell.
Term
Too many mouths
Definition
A mutation in Arabidopsis that causes the plant to have four stomata where it should have one.
Term
Torpedo stage
Definition
The fifth stage in embryogenesis. Cotyledons and axis elongate, and the primary meristem extends with them. The embryo may become curved. In monocots the cotyledon often becomes the largest structure in the embryo. The suspensor undergoes programmed cell death.
Term
Torus
Definition

Plural: tori

A thickened central portion of the pit membrane of the tracheids of softwoods. May enlarge and block the tracheid.

Term
Totipotent
Definition
Cells that have the ability to become embryonic and produce a full plant.
Term
Tracheary elements
Definition
The cells of xylem tissue. Elongated, lack protoplasts at maturity, an dhave pits in their walls. During development, secondary wall thickenings are deposited in rings or spirals, allowing for stretching after differentiation. In secondary xylem they cannot be stretched. Have programmed cell death that eliminates the protoplast. There are two types: tracheids, and vessel elements.
Term
Tracheid
Definition
A tracheary element. Lacks perforations. The principle water-conducting cell in gymnosperms and seedless vascular plants. Water passes through pit membranes, blocking out air bubbles. Longer than vessel elements, with tapered ends. Has a high surface area to volume ratio that holds water up against gravity.
Term
Tracheophytes
Definition

Vascular plants

Includes seedless and seed plants.

Term
Trans face
Definition
The maturing side of the Golgi body. Faces towards the plasma membrane.
Term
Transfer cells
Definition
Parenchyma cells with increased surface area of the plasma membrane. Facilitates movement of solutes over short distances: uptake or secretion. Occurs in association with xylem and phloem of small veins in cotyledons, leaf traces at nodes, reproductive structures, glandular structures, and in the leaves of herbaceous eudicots.
Term
Transition vesicle
Definition
Flows from the ER to the cis face of the Golgi body. Transports glycoproteins.
Term
Transitional region
Definition
The region of the plant axis where it transitions, gradually, from the vascular bundles in the root (central stand) to that in the shoot (bundles). Transition is initiated as the procambial system appears in the embryo.  Structure of the transitional region differs between plant types.
Term
Transmitting tissue
Definition
Cells in the style that guide pollen tubes towards the ovule.
Term
Transpiration
Definition
Plants releasing water vapour into the atmosphere.
Term
Tree of life
Definition
A depiction of the genealogic releationship of all organisms to a single ancestral species.
Term
Trichome
Definition
A type of epidermal cell. An appendage. Has a variety of functions. Reflects solar radiation, reduces plant temperature, reduces water loss, secretes toxic substances, defense against insects, traps insect prey, chemical defense. Includes root hairs.
Term
Trimerophytophyta
Definition
An extinct phyla of seedless vascular plants. Went extinct by the Devonian period, 360 million years ago.
Term
Triple fusion
Definition
Fusion of a sperm cell with two polar nuclei to form the triploid primary endosperm nucleus.
Term
Tropsim
Definition
Responses to environmental cues. Includes phototropism and hydrotropism.
Term
TTG
Definition

TRANSPARENTTESTA GLABRA

Inhibits prodotermal cells brodering trichomes from becoming trichomes. Mutants lack trichomes on aerial parts, but have extra root hairs.

Term
Tube cell
Definition

One of the cells in a gymnosperm pollen grain.

The larger cell formed in the two-celled stage of microgametogenesis in angiosperms.

Term
Tuber
Definition
The most familiar type of storage stem. Example: potato.
Term
Tubulin
Definition
The subunits that arrange into protofilaments that form microtubules.
Term
Tunica
Definition
A region of the shoot apical meristem in tunica-corpus organization. The outermost layer. Divides anticlinally. Contributes to the surface growth without increasing the number of cell layers in the meristem. The number of tunica layers varies with species. Layers are denoted as L1, L2, and L3. The protoderm always originates from the tunica.
Term
Tunica-corpus organization
Definition
The organization of the shoot apical meristem in most angiosperms. There is a tunica and a corpus region.
Term
Turgor pressure
Definition

Pressure of the tonoplast.

Early plants could only stand erect by turgor pressure. Not very strong, and limited their stature and the environment where they could live.

Term
Turpines
Definition
Secondary metabolites in tomatoes. Kills bugs. Created by glandular trichomes.
Term
Two-celled stage
Definition

Pollen mitosis I

The first stage of microsporogenesis. The microspore divides to form the vegetative cell and generative cell. In most angiosperms, pollen is dehisced from the anther at this stage.

Term
Type specimen
Definition
A dried plant specimen housed in a museum or herbarium. Each species has one.
Term
Tyloses
Definition
Balloon-like outgrowths from ray or axial parenchyma cells through pit cavities in the vessel walls of woods. Formed when the vessel becomes non-functional. May block the vessel. Often induced to prevent the spread of pathogens.
Term
Ulva
Definition

Sea lettuce

A genera of Ulvophyceae. A flat thallus two cells thick and up to a meter long. Anchored to substrate by a holdfast. Each cell has one chloroplast and one nucleus. Has isomorphic generations, but one mating type of the gametophytes is larger than the other.

Term
Ulvophyceae
Definition
Primarily marine algae (some freshwater). Filamentous or in flat sheets of cells. The only algae with sporic meiosis. Includes Cladophora, Ulva, and siphonous marine algae.
Term
Underleaves
Definition
Smaller leaves in a row on the lower surface of a leafy liverwort.
Term
Unisexual gametophyte
Definition
Sperm-producing antheridia and egg-producing archegonia are on separate gametophytes. Heterosporous.
Term
Vacuole
Definition

Liquid filled cavities. There is one or more in the cell. May originate from the ER or Golgi apparatus.

A single, very large vacuole is a tonoplast.

Term
Vascular cambium
Definition

A lateral meristem. Highly vacuoled cells. The same in the roots as in the stem. Has periclinal division that produces secondary xylem and phloem. Xylem is produced towards the inseide, and phloem is produced towards the outside. More xylem is produced than phloem because phloem is pushed outwards and destroyed.

Dormant during the winter, and is reactivated in the spring by auxin. 

Many tropical trees have continously growing vascular cambium. Includes fusiform initials and ray initials.

Term
Vascular cylinder
Definition

Stele

Consists of primary vascular tissues and the pericycle.

Term
Vascular plants
Definition
With water-conducting vessels xylem and phloem. All phyla in Plantae except bryophytes are vascular. Taller plants, in terrestrial habitats: rely on groundwater from the soil. Water transports from roots to stems to leaves via the vascular system. Upward growth required adaptations for water retention, structural support, dispersal of spores, and fusion of gametes.
Term
Vascular rays
Definition
The radial system. Consists of ray cells produced by the ray initials of the vascular cambium. A pathway for movement of food and water between secondary phloem and xylem.
Term
Vascular tissue system
Definition
A fundamental tissue system in vascular plants. Originates from the procambium. Embedded in ground tissue. Has complex tissues. A continuous system of conducting tissues. A step in the evolution of vascular plants. There are two tissues: xylem and phloem.
Term
Vein
Definition

Vascular bundle

Vascular tissues that permeate the leaf, containing xylem and phloem. Venation is netted or parallel. There are minor and major veins.

Term
Venter
Definition
A component of an archegonia. Surrounds the egg. After fertilization it enlarges to contain the young sporophyte, becoming the calyptra.
Term
Ventricaria
Definition

Valonia

A member of Codium. Common in tropical waters. Used in studies of cell walls and physiologcial experiments. Unicellular, but large, multinucleate. Attached to the substrate by several rhizoids. About the size of a hen's egg.

Term
Vesicle
Definition
A component of the endomembrane system. Includes transition, shuttle, and coated vesicles.
Term
Vessel
Definition
A long, continuous column of vessel elements, connected at their perforation plates.
Term
Vessel element
Definition
A tracheary element. Evolved independently in many groups of vascular plants. Not found in seedless vascular plants and gymnosperms. More efficient conduction of water than tracheids, but air bubbles can obstruct the flow of water. Wider than tracheids. Contain perforations on perforation plates that are aligned end to end to form the vessel.
Term
Volvox
Definition
A multicellular, motile chlorophyte. Forms a spheroid a single layer thick. Consists of 500 - 60,000 vegetative, biflagellated, photosynthetic cells, and a few non-flagellated reproductive cells. Reproduces sexually by forming juvenile spheroids on the inside, which hatch by releasing enzymes that dissolve the parent. Sexual reproduction is triggered by a glycoprotein released into the population.
Term
Vorticella
Definition
A protozoan which has endosymbiont Chlorella bacteria living inside it, performing photosynthesis.
Term
Water-borne fruits
Definition
Some fruits are adapted to float: air is trapped in some part, or the tissues have large air spaces. Some fruits float in ocean currents, including the coconut. Rainwater run-off disperses seeds on hillsides and mountain slopes.
Term
Water cycle
Definition
A use for plants. Plants move water from the soil to the atmosphere by transpiration. This purifies the water.
Term
Water retention
Definition
An adaptation that was necessary for vascular plants. Cuticles prevent desiccation and stomata regulate water and gas exchange.
Term
Waxes
Definition
A component of the cell wall. Reduces water loss. Occurs only in combination with cutin or suberin.
Term
Wet stigma
Definition
A stigma with glandular tissue that secretes proteins, amino acids, and lipids.
Term
White campion
Definition
A flower which is pollinated by nocturnal moths. Produces benzaldahyde to attract moths.
Term
Whorl
Definition
A circle of flower parts of one kind. They are (from outside in): calyx, corolla, androecium, and gynoecium.
Term
Whorled
Definition
A phyllotaxy. There are three or more leaves at each node. Example: Culver's-root.
Term
Wind-borne fruits
Definition
May be small and dustlike, have wings formed from the perianth, or have a plume-like pappus that aids in keeping seeds aloft. In some plants the seed has a plume rather than the fruit. Some seeds have hairs. In tumbleweeds the whole plant or portions of the plant are blown by the wind, scattering seeds. Some fruits are deshisced from the plant at high speeds, throwing them as far as 15 m from the plant.
Term
Wind pollination
Definition
A type of pollination. No nectar is produced. Flowers are dull in colour and relatively odorless. Petals are small or absent. Often unisexual. Occurs in temperate regions where many plants of the same species grow. Pollen dehiscence often occurs in the spring. Well-exposed anthers and stigma.
Term
Winter annual
Definition
A biennial which germinates in the fall, survives the winter, and finishes its life cycle in the spring.
Term
Wood
Definition

Secondary xylem

Used for shelter, fuel, building of tools, paper, and many other things. Includes hardwoods and softwoods.

Term
Wound callose
Definition
The majority of callose observed in a sieve element. Deposited due to injury during preparation of the microscope slide.
Term
WUS
Definition

WUSCHEL

First expressed at 16-cell stage of embryo development. Necessary for establishment of a root apical meristem, and forms maintenance of initial cell function. Expressed in the organizing centre and persists through shoot development. With lost of WUS, function initials differentiate.

Term
W. W. Garner and H.A. Allard
Definition
USDA officers that discovered photoperiodism in the 1920's.
Term
Xerophytes
Definition
Plants adapted to arid habitats. Usually have more stomata than other plants, to permit higher rate of gas exchange during rare periods of favourable water supply. Stomata are often found in stomatal crypts. There may be a thick layer of trichomes which may secrete resins that prevent water loss. Palisate parenchyma may appear on both sides of the leaf.
Term
Xylem tissue
Definition
A vascular tissue. Conducts water and minerals. Cells are tracheary elements. Supports the plant body. It is derived from the procambium. In the secondary plant body, it is derived from teh vascular cambium. Contains some parenchyma cells, occuring in vertical strands in the primary xylem, and in rays in the secondary xylem, which store substances. May also contain fibres and/or sclereids, for support and storage, some living at maturity.
Term
Young sporophyte
Definition
The early stages of the sporophyte in byrophytes.
Term
Zoospores
Definition
The spores of chlorophytes.
Term
Zosterophyllophyta
Definition
An extince phyla of seedless vascular plants. Went extenct by the Devonian period, 360 million years ago.
Term
Zygote
Definition
Diploid, single-celled stage of sporic meiosis. Formed when a male and female gamete fertilize together. Develops into the sporophyte. In bryophytes and ferns it develops inside the archegonia, using energy from matrotrophy. In angiosperms it develops into the embryo.
Term
Zygotic meiosis
Definition
An alteration of generations, found in Chlamydomonas and fungi. The zygote divides by meiosis, forming four haploid cells. The haploid cells form a multi-cellular organism that gives rise to gametes by differentiation. The zygote is the only diploid cell.
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