Transcript Parts of the plantStems

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
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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
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Parallel leaf veins
Scattered vascular bundles
Flowers in parts of 3's
One cotyledon (seed leaf)
Characteristics of Dicots
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Branched leaf veins
Continuous vascular bundles
Flower Parts in 4's or 5's
Two cotyledons (seed leaves)
Internal Stem Structure
Internal Stem Structure
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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
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Because the cambium produces new
cells for xylem and phloem, a tree
continues to increase in width year after
year.
Internal Stem Structure
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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
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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
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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.