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Tissues and growth of stems (Stem Growth and Differentiation (subapical…
Tissues and growth of stems
Stem Growth and Differentiation
protoderm
early cells of differentiation
subapical meristem
metaxylem
largest tracheary elements of all
cells dividing and growing
just below apical meristem
protoxylem
constitute 1st xylems
Apical meristems
cells divide by mitosis and cytokenisis
pro vascular tissues
young xylem and phyloem cells
Internal Organization of stems
Vascular Bundles
pith
parenchyma similar to the cortex
collateral
Xyloem and phloem parallel
Primary phloem
mixed with sieve elements and companion cells
storage parenchyma and mechanical sclerenchyma
Epidermis
outer walls encrusted with cutin
Defense again fungi, bacteria
layer of wax may be present
inhibit CO2 entry
builds up to make cuticle
Prevents loss of water to air
Single layer of parenchyma cells
guard cells
open during daytime
stoma
allow entry of CO2
swell with water
Cortex
fit compactly
photosynthetic parenchyme
allows for buoyancy
sometimes collenchyma
Vacular Tissues
Phloem
sieve tube members
sieve elements
parenchyma cells
nuclie degenerate but cell stays alive
shorter than the plant
sieve cells
Xylem
secondary wall impermeable to water
Primary wall uncovered
water makes it collapse inward
Water and minerals enter
vessel elements
plasmodesmata in walls
entire stack is a vessel
must get water from parenchyma
perforation
each element must have 2
tracheids
External Organization of stems
nodes
internodes
region between nodes
leaves attached
shoot
stem + flowers, leaves, buds
Rhizomes
allow plants to spread underground
tubulers
"potatoes"
Stem
Stolons "runners"
leaves dont expand
Internodes long and thin
Phyllotaxy
Positions leaves so not shading one another
axis
leaf axil
area above leaf attachment
auxiliary bud
Miniature shoot
Types of Cells and tusues
Collenchyma
Primary walls
Tips elongate
collenchyma can be streched
Thick in some places
Thin in some places
wall exhibits plasticity
require more glucose
Produced in shoot tips, young petioles
Parenchyma
Some die and maturity
Glandular cells
Secrete
mucilage
oils
fragrances
resins
nectar
Thin walls
few chloroplasts
Transfer cells
Mediate short transport
large plasma membrane
large-scale molecular pumping
Most Common cell type
Chlorenchyma cells
Involved in photosynthesis
Numerous chloroplasts
Active metabolically
Only thin primary walls
Sclerenchyma
Primary wall
Elastic
can be deformed
return to original size
Conducting Sclerenchyma
Mechanical Sclerenchyma
Short sclereids
produced by cell division
hard, impenetrable
pits of peaches
shells of walmuts
Brittle and inflexible
Long fibers
found in wood
Elastic secondary walls
Flexible
secondary wall
almost always lignified
Develop from parenchyma cells