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Tissues & Primary Growth of Stems (External Organization of Stems…
Tissues & Primary Growth of Stems
Plant Classification
angiosperms
basal angiosperms
waterlillies
magnolias
laurels
eudicots
roses
asters
maples
monocots
grasses
lilies
cattails
palms
philodendrons
bromeliads
Types of Cells & Tissues
parenchyma
only primary walls-remain thin
parenchyma tissue=mass of parenchyma cells
most common type of cell and tissue
constitute all soft plant parts
make up soft leaves, petals, fruits, and seeds
actively metabolic
chlorenchyma cells
involved in photosynthesis
have numerous chloroplasts
thin walls to allow CO2 to come in
glandular cells
secrete nectar, fragrances, mucilage, resins, and oils
have elevated amounts of dictyosomes & endoplasmic reticulum
transports lots of sugar & minerals into themselves - to transport the product out
transport cells
mediate short distance transport of materials - using large, extensive plasma membrane
increase their surface area
have knobs, ridges and ingrowths on inner surface
allows lots of molecular pumping
phloem=parenchyma tissue conducting nutrients over long distances
inexpensive to make
collenchyma
primary cell wall - thin & thick (corners) in certain areas
have plasticity
usually produced in shoot tips
stay at size when stretched
sclerenchyma
has both primary & a thick secondary wall
walls are elastic
return to original size after stretching
develop from parenchyma cells in mature organs
supports plant with its strength
don't droop if wilted
conducting sclerenchyma
tracheids
found in all vascular plants
vessel elements
found almost exclusively in flowering plants
mechanical sclerenchyma
long fibers
area of strength & flexibility
short sclereids
brittle & inflexible
shells of walnuts
shell of coconut
pits and stones of cherries & peaches
living sclereids often help store starch
pits are made in the secondary wall (a pit-pair=two pits)
External Organization of Stems
stem=is an axis
shoot=stem + any leaves, flowers, or buds
flowering plants :<3:
nodes=where leaves are attached
internodes=regions between nodes
short internodes= cabbage, lettuce, & onions
wide internodes= asparagus
narrow internodes= alfalfa sprouts
long internodes= vines
leaf axil=stem area above the point where leaf attaches
axillary bud=inside the leaf axil
waxy bud scales=modified leaves to protect inside organs
terminal bud=at tip of each stem
phyllotaxy
=the arrangement of leaves on the stem
important so leaves don't shade each other
two leaves per node=
opposite phyllotaxy
three or more leaves per node=
whorled
distichous phyllotaxy
= leaves arranged in only 2 rows
decussate phyllotaxy
= leaves are arranged in four rows
spiral phyllotaxy
= each leaf is located slightly to the side of the ones immediately above & below it=leaves form a spiral up the stem
one leaf per node=
alternate phyllotaxy
Variety
stolons
= long & thin internodes
bulbs
= short shoots, thick leaves
onions, daffodils, garlic
corms
= vertical, thick stems with thin leaves
crocus and gladiolus
rhizomes
= fleshy horizontal stems that spread underground
bamboo, irises, and canna lilies
tubers
= horizontal and grow for a short time, mainly storing nutrients
potatoes
perennials
= tubers, corms, bulbs, & rhizomes
store nutrients to re-grow after dormancy
subterranean location for protection
a plant will not always be stolons, or rhizomes, they will have a combination
:!!: :!!:
Internal Organization of Stems: Arrangement of Primary Tissues
:explode:
Epidermis
epidermis=outermost surface of an herbaceous stem
epidermis= single layer of living parenchyma cells
for protection & prevention of water loss
outer tangential walls have
cutin
=a fatty substance that makes it impermeable to water
pure layer of cutin=
cuticle
cutin & wax resist digestive enzymes & provide defense against fungi and bacteria
guard cells & stomatal pores=
stoma
stomata
can be open during day to allow CO2 into plant
after sunset most plants shut their stomata to prevent water loss
trichomes
= elongated epidermal cells. Also called
hairs
:
make it hard for animals to land on, walk on, or chew into
allows water molecules to go back into stoma
can act as secretory glands
protoderm
=cells that are in early stages of differentiation
Cortex
interior to epidermis
composed of parenchyma and sometimes collenchyma
mostly compact but can be open with intercellular air spaces
Vascular Tissue
Xylem
water & minerals enter in roots and are conducted up to leaves and stems
sap travels through dead, hollow cells
water evaporates from surface of stems, leaves, and flowers
tracheids & vessel elements= tracheary element
cells must enter cycle arrest and stop dividing
annular thickenings
= organized set of rings on the primary wall
annular thickenings
provide more surface area
helical thickenings
= secondary wall exists as 1 to 3 helices interior to the primary wall
scalariform thickening
= stronger wall structure
reticulate thickening
= secondary wall is deposited in the shape of a net
circular bordered pits
=strongest tracheary element=virtually all of the primary wall is underlain by secondary wall
have a border to provide extra wall material due to pits
tracheids get their water from the tracheids below them
pit membrane
=aligned set or pit-pairs with middle lamina
pit membrane is very permeable to water
vessel elements
same as tracheids except an entire region of both primary & secondary wall is missing
during differentiation a perforation is digested through a site of primary wall, often removing the entire end wall
water passes through these perforations from one vessel to next
an entrie stack of vessel elements=
vessel
Phloem
cells are living
sieve cells are associated with albuminous cells and sieve tube members are controlled by companion cells
this is how they work without their nuclei
companion cells load sugars into and out of the sieve tube members
pick up sugar where it's abundant and transports it to areas where the sugar is needed (growing areas)
water is transported at the same time as sugar
sieve cells & sieve tube members=
conducting cells
=
sieve elements
have only primary walls
are parenchyma cells
sieve pores
= when immature sieve elements enlarge their plasmodesmata
groups of sieve pores=
sieve areas
conducts mostly longitudinally
sieve tube
=large on the two ends of a cell & have wide sieve pores at the ends as well
sieve plates
=end-wall sieve areas with large sieve pores
nuclei degenerate but the cells remain alive
Vascular Bundles
xylem & phloem together
bundles are arranged in one ring surrounding the pit in basal angiosperms, eudicots
in monocots, bundles are distributed as a complex network in the inner part of the stem
all bundles are collateral= each contains both xylem (primary xylem) and phloem (primary phloem) running parallel
primary xylem cells are larger than primary phloem cells
provscular tissues
=young cells of xylem & phloem
Stem Growth & Differentiation
apical meristems
= region where stems grow longer
subapical meristem
= just below apical meristem. Its cells are dividing & growing for the region below
protoxylem
=first xylem to appear. Cells around them grow & expand
metaxylem
= largest tracheary elements
protophloem
=exterior cells maturing
metaphloem
=cells closest to metaxylem
Primary tissues
=the tissues produces by apical meristems
Primary growth
= the growth & tissue formation that results from apical meristem activity
Plant Body Types
herb=never becomes woody with bark
<one year=snapdragons
<one year=petunias
<one year=beans
<one year=corn
<one year=wheat
more than one year=irises
more than one year=lilies
herbaceous=primary plant body :
woody=secondary plant body
