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Chapter 5 (external organization of stems (phyllotaxy is the arrangement…
Chapter 5
external organization of stems
stem is an axis
shoot is the stem plus the leaves
nodes are where leaves are attached
internodes are the regions between the nodes
leaf axil is the stem area just above the point where a leaf attaches
axillary bud is a miniature shoot with a dormant apical meristem and several young leaves
bud scales are the small, corky, waxy stuff that is covering the bud
terminal bud is the extreme tip of each stem
phyllotaxy is the arrangement of leaves on a stem
bulbs are short shoots that have thick, fleshy leaves
corms are vertical, thick stems that have thin leaves
rhizomes are fleshy horizontal stems that allow a plant to spread underground
tubers are like rhizomes that grow for a short period of time to store nutrients (like a potato)
internal organization of stems: arrangement of primary tissues
epidermis
outermost surface of an herbaceous stem
single layer of living parenchyma
encrusted in cutin (a fatty substance that makes the wall impermeable to water)
cortex
interior to the epidermis
composed of photosynthetic parenchyma and sometimes collenchyma
fit together compactly
vascular tissues
xylem
tracheids
vessel
water and minerals enter in the roots and pushed upwards through the leaves and stems
passes through dead cells not alive
phloem
pick up sugar from where it is abundant and transport it to where it is needed
carries sugar to the fruits and into the storage organs of perennial plants
not a circulatory system
vascular bundles
arranged in one ring surrounding the pith, a region of parenchyma similar to the cortex
are collateral, contains both xylem and phloem strands
basic types of cells and tissues
parenchyma
cells have only primary walls that remain thin
parenchyma tissue is a mass of parenchyma cells
most common
active metabolically and some remain alive after they mature
chlorenchyma
parenchyma cells involved in photosynthesis
have numerous chloroplasts
thin walls to allow light and carbon dioxide to pass through
glandular cells
secrete nectar, fragrences, mucilage, resins. and oils
are also parenchyma cells
contain few chloroplasts and large amounts of dictyosomes and endoplasmic reticulum
transport large quantities of sugar and minerals into themselves, transform them metabolically and transport them out
transfer cells
mediate short distance transport of material
has large, extensive plasma membrane capable of holding numerous molecular pumps
collenchyma
primary wall that remains thin in some areas but thick in others (mostly the corners)
is claylike, able to be reformed and deformed with pressure
is found near shoot tips (vines for grapes)
present as a layer under epidermis or as bands located next to vascular bundles, making the tips stronger
require more glucose for their production
sclerenchyma
has a thick primary and secondary wall
both walls are elastic, meaning they can be deformed but pop back to their original shape
can develop from parenchyma cells
conducting
mechanical
long fibers
short sclereids
