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Tissues and the Primary Growth of Stems (External Organization of Stems…
Tissues and the Primary Growth of Stems
Upright plants gather sunlight better
Elevated cells aren't in contact with moisture in mud and need water transported to them
Stems
Elevated cells need support
Result of the need for stem support
Angiosperms (Flowering Plants)
Types
Basal Angiosperms
Most primitive of Angiosperms
Eudicots
Broadleaf
Also known as Dicots
Monocots
Members of Class
Liliopsida
Magnoliophyta
Largest Division in Plant Kingdom
Basic Types of Cells and Tissues
Parenchyma
Thin Cell Walls
Most Common
Alive Upon Maturity
Soft Part of Plant
Highly Specialized
Types of Parenchyma Cells/Tissue
Chlorenchyma
Specialized for Photosynthesis
Particularly Numerous Chloroplasts
Thin cell walls to allow light and carbon dioxide in
Glandular
Specialize in Secretion
Nectar
Fragrances
Mucilage
Resins
Oils
Elevated amounts of dictyosomes and endoplasmic reticulum
Fewer Chloroplasts
Transports sugar and minerals in, transforms them, then transports them out
Transfer
Transport by plasma membrane capable of holding numerous molecular pumps
Collenchyma
Cell wall has varying levels of thickness depending on the specific area
Malleable
Requires more glucose for production
Sclerenchyma
Primary wall and thick secondary wall
Elastic
Supports plant by strength alone
Types of Sclerenchyma Cells/Tissue
Fibers
Long
Some dead, some alive upon maturity
Sclereids
Spherical
Usually dead upon reaching maturity
External Organization of Stems
Shoot
Comprised of the stem along with any leaves, flowers, or buds
Types of Shoots
VInes
Use of extended internodes to 'explore' environment
Support is provided by tendrils in some species
i.e.
Antigonon leptopus
Both are rare examples of plants displaying independent movement
Stolons
Also known as runners
Has the ability to extend long distances without using many nutrients
Due to long and thin internodes
Airplane plant (
Chlorophytum
) uses it's stolons to hold itself up, presumably to get in favorable sunlight
Bulbs
Short with thick and fleshy leaves
Equal in evolutionary fitness
Corms
Tall and thick with thin and papery leaves
Rhizomes
Fleshy stems that allow for additional underground development
Bamboo, irises, and canna lilies
Tubers
Like Rhizomes, but only store nutrients underground
Potatoes
Base is called trunk
Nodes
Area leaves are attached
Internodes
Area Between Nodes
Leaf Axil
Stem area right above leaf
Contains Axillary Bud
Vegetative bud if it grows into a branch
Floral bud if it grows into a flower or group of flowers
Protected by bud scales
Has a terminal bud at the extreme tip of each stem
Phyllotaxy
Alternate: 1 leaf per node
Opposite: 2 leaves per node
Decussate: Leaves located in 4 rows
Whorled: 3 leaves per node
Spiral: Leaves not aligned with closest neighbor
Distichous: Leaves located in 2 rows
Epidermis
Outermost surface of the stem
Composed of living parenchyma cells
Responsible for all materials coming in and out of the plant
Most importantly, water
Outermost part is called the cuticle
Named for the fatty substance cutin that coats this area
Benefit of cutin is impermeability to water
Downside is the hard time plants have obtaining Carbon Dioxide through Epidermis
Guard cells
Compensates for downside
Lets in Carbon Dioxide during the day
Makes up the stoma that appear across the epidermis, along with the stomatal pore between them
Some epidermal cells become trichomes
A.K.A. Hairs
Makes it a bit harder for animals to destroy leaves
Cortex
Composed of photosynthetic parenchyma and collenchyma in most plants
Second layer, next to Epidermis
Compact
Vascular Tissue
Xylem
Tracheids
Long, straw-like vascular cells
Deals with blockages more effectively
Ends Pointed
Vessel Elements
Much wider than tracheids
Usually Ends Flat
Entire stack is simply called a vessel
Phloem
Sieve Cells
Similar shape to tracheid
More Primitive
Sieve Tube Members
Has a companion cell that controls it
