Stems Parts of the Plant: Stems 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

● 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.