View
233
Download
0
Category
Preview:
Citation preview
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
• 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.
Recommended