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Tissues and Stems (External Stem (Types of stems (Rhizomes (fleshy…
Tissues and Stems
External Stem
nodes
where the leaves are attached
internodes
region between nodes
leaf axil
stem area just above where leaves attach
axillary bud
miniature shoot with a dormant apical meristem
bud scales
protects delicate organs inside
terminal bud
extreme tip of stem
Phyllotaxy
arrangement of leaves
alternate
leaves one per node
Opposite
leaves two per node
decussate
leaves located in four rows
Whorled
three or more leaves per node
spiral
leaves not aligned
distichous
leaves located in two rows only
Types of stems
Rhizomes
fleshy horizontal stems
allow to spread underground
Tubers
horizontal like Rhizomes
grow for short time period
store nutrients
Internal Organization
Epidermis
outermost surface
single layer of living parenchyma cells
outer tangential walls encrusted with cutin
a fatty substance that makes wall impermeable
builds up as a more or less pure layer called the cuticle
contain guard cells
with a stomatal pore between them
these two form a stoma
most plants are elogated outwards and become trichomes or hairs
Cortex
interior to the epidermis
composed of parenchyma and sometimes collenchyma cells
Vascular Tissues
two types
Xylem
conducts water and minerals
Phloem
distributes minerals and sugars
not like the circulatory system in animals
assemblage of conducting tissues and associated supportive fibres
Xylem
Tracheids
Vessel Elements
annular thickenings
small amount of secondary wall organized in rings
helical thickening
the secondary wall exists as one to three helices
scaliriform thickening
provides strength to the secondary wall
reticulate thickening
the secondary wall is deposited in the shape of a net
Phloem
Sleve Cells
long and narrow
ends pointed
sleve areas are small and located all over
albuminous cells
all non angiosperm vascular plants
Sleve tube members
short and wide
ends usually flat
sleve areas are on side walls small
sleve areas on end walls large
companion cells
angiosperms only
Stem Growth and Differentiations
Apical Meristems
Growth that originates in the apical meristem is called primary growth
the tip of a plant shoot or root that produces auxin and causes the shoot or root to increase in length
subapical meristems
region below apical meristems
cells are dividing and growing for region below
protoxylem
first xylem to develop
usually distinguished by narrower vessels formed of smaller cells.
metaxylem
istinguished typically by broader tracheids and vessels with pitted or reticulate walls
part of the primary xylem that differentiates after the protoxylem
Tissues
Collenchyma
have a primary wall
exhibits plasticity
elongating shooting tips
long and flexible
under epidermis
or bands next to vascular bundles
cell walls are thick
more glucose for production
Parenchyma
primary walls very thin
parenchyma tissue is a mass of parenchyma cells
most common type of cell and tissue
chlorenchyma cells are parenchyma cells in photosynthesis
numerous chloroplasts
other types are pigmented cells
glandular cells are also parenchyma cells
secrete nectar, fragrances and oils
transfer cells
another parenchyma cell
mediate short distance transport
some function by dying at maturity
Sclerenchyma
primary wall and thick secondary wall
the walls are elastic
develop from parenchyma cells
conducting sclerenchyma
Trachieds & Vessel elements
mechanical sclerenchyma
Sclerids & Fibers
