Parts of the Plant: StemsStems

Most consistent identification characteristic

Functions of Stems

• Stems have 2 main functions:

• 1) The movement of materials, such as water and minerals from roots up to the leaves; and manufactured food from the leaves down to the roots.

• 2) Supports the leaves and reproductive structures (i.e.: flowers, fruit, seed)

Functions of Stems continued

• In some plants, but not all plants...

• 3) photosynthesis in green stemmed plants

• 4) Food storage (i.e.: Irish Potato)

• 5) Reproduction (stem cuttings, grafting…)

The Anatomy of a Stem

• Terminal Bud – point of new growth• will be stem tissue or flower• Axillary Bud – dormant bud May become • new leaves or stem.• Leaf Scar – point where leaf was once • attached.• Bud Scale Scar –Shows where a terminal

was attached. • Lenticel - allows the exchange of gases.

Anatomy of Stems

Stems take on many different modifications or forms (modified stems)

Above Ground Modifications:

Crowns – very short stem

at the surface of the soil.

Stolons – (runners) side stems

growing laterally at the surface

of the soil.

Anatomy of Stems

• Spurs – tiny, pin-like stems

• Tendrils – enable plant to anchor to support structures by wrapping around

• Thorns – large wedge stems, coming to a sharp tip

Anatomy of Stems

• Below Ground Modifications:• Bulbs – rounded, storage• structures

Corms – rounded, flat,storage structures

• Rhizomes – side stems growing laterally below

ground

• Tuberstems – large, underground storage

system

Types of Stems

• Woody Stems – stems that have a corky outer covering (bark)

Types of Stems

Herbaceous stems – plants that have stems that are soft and fleshy tissue.

• Vascular Tissue – specialized tissue that provides support of plants and transport of materials up and down the plant.

• Phloem [flow-em]- moves manufactured food down the stem for storage.

• Xylem [zi-lim] – moves moisture and minerals up the stem.

• Vascular plants are divided into 2 groups called Gymnosperms and Angiosperms.

• Angiosperms also are divided into 2 groups:

• Monocotyledons• Dicotyledons

Characteristics of Monocots

• Parallel leaf veins• Scattered vascular bundles• Flowers in parts of 3's• One cotyledon (seed leaf)

Characteristics of Dicots

• Branched leaf veins

• Continuous vascular bundles

• Flower Parts in 4's or 5's

• Two cotyledons (seed leaves)

Internal Stem Structure

Internal Stem Structure

● Woody Dicot Plants have vascular tissue forming in concentric rings.

● A corky outer layer called bark protects the vascular tissue. It is:

● Phloem is located inside the corky bark.● Cambium is the next layer. It is meristem

tissue that produces new cells for the phloem and the

● Xylem. This layer is also known as wood

● Because the cambium produces new cells for xylem and phloem, a tree continues to increase in width year after year.

Internal Stem Structure

● Monocot plants form their internal stems in bundles of tubes in random order in the stem.

● Each tube bundles both phloem and xylem tubes together.

● All cells are formed in the early stages of growth. No cambium in a mature plant stem.

● A mature stem is achieved by cell enlargement. No new cells are produced

Internal Stem Structure

● Herbaceous Dicot Stems have phloem, xylem and cambium although the cambium disappears after maturity.

● The three parts of the system line up in a ring form but not as strong as the woody stem.

● Herbaceous means soft fleshy tissue.

Summary

● The ring system of tissue in woody dicots can support a large amount of weight.

● The random order of tubes in moncot and dicot herbaceous stems cannot support large amounts of weight;

● They cannot therefore, get very large.