Functions of Stems

1. Support above ground plant parts

2. Add new tissue to the plant body

3. Transport substances

4. Storage in some cases

5.  Photosynthesis if above ground and gree

Terminal or apical bud

Axillary Bud

or

Lateral Bud

Marks on a woody stem that show were the terminal bud scales were after they have fallen off.

Terminal bud scale scars show how long the stem grew in one year.

How do you recognize a monocot stem?

The vascular bundles are widely scattered.

Ground tissue

The parenchyma cells that surround the vascular bundles in a monocot stem

How do you recognize a eudicot stem?

The vascular bundles are arranged in a ring.

Which kind of stem will undergo secondary growth,  monocot or a eudicot?

Only eudicot stems have secondary growth.

Vascular cambium

A layer of dividing or meristematic cells that forms between the xylem and phloem in eudicot stems.

What kind of cells does the vascular cambium make?

The vascular cambium makes secondary xylem to the inside and secondary phloem to the outside.

Wood

Another name for secondary xylem

Bark

Another name for secondary phloem.

All of the tissue from the vascular cambium to the outer surface of the stem.

What does xylem transport?

Is it alive?

Xylem transport water.

It is dead.

What does phloem transport?

Is it alive?

Phloem transports sugars.

It is alive.

Which tissue layer accumulates?

Why?

Secondary xlyem accumulates, not phloem.

Since the vascular cambium makes new cells in two directions, as the xylem accumulates, it stretches the outer layers of secondary phloem.  They crack apart, and are shed.

Lenticel

A spongy layer in the bark that allows for gas exchange.

Cork Cambium

 A new cambium layer that forms in the secondary phloem.

What does the cork cambium make?

It makes cork cells to the outside and cork parenchyma toward the inside. 

The cork cambium cells and the cork parenchyma cells are living cells.

Cork cells

Layer of cells made by the cork cambium.

They replace the epidermis.

They are filled with suberin, a waterproofing substance.

They will eventually die.

Why do different kinds of trees have bark layers that are shaped differently: smooth or rough?

The texture of bark is determined by the shape of the cork cambium.  If it forms in a continuous ring, the bark will be smooth.

If it forms in overlapping arcs, the bark will be scaly.

Periderm

All of the cell layers made by the cork cambium.

The outer layer of the bark.

Springwood

The first xylem cells made by the vascular cambium in the spring.

These cells are big - so they are light in color.

Summerwood

The xylem cells made by the vascular cambium in the late summer.

They are small in size so they look dark.

The cambium will stop making new cells in the autumn as the tree goes dormant through the winter.

A layer of wood that forms every growing season; we can see it because of the difference in color between springwood and summerwood.

How can we determine the age of a tree?

By counting the tree rings.

Heartwood

The wood at the very center of a tree trunk.

It can be darker than the other wood.

Sapwood

The wood just underneath the bark.  It is the youngest wood and it transports water.

Hardwood

Wood made by angiosperms - flowering trees.

It has vessel elements so it is hard.

Think of oak flooring.

Softwood

Wood made by conifers.

It only contains tracheids so it is softer.

Think of pine wood.

Dendrochronology

Using tree rings to study past events.

What can dendrochronology be used for?

It can tell us about past weather conditions.

It can be used to determine the age of wooden objects.

It can be used to determine where in the world a wooden object is from.

How old is the tree in the previous card?

We can see three layers of secondary xylem so it is 3 years old.

How do the stems of a maple tree and a poison ivy vine differ?

The tree has a thick, strong stem that can support the plant.

The vine has a thin, weak stem that cannot support the plant by itself; it must climb up a pole or another plant like a tree.