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Tissue and the primary growth of stems (phyllotaxy (Alternate: leaves one…
Tissue and the primary growth of stems
basic types of cells and tissues
parenchyma
thin primary walls
typically alive at maturity and performs many function
collenchyma
unevenly thickened primary walls
typically alive at maturity
provide plastic support
sclerenchyma
primary walls plus secondary walls.
many dead at maturity
provide elastic support and some are involved in water transport.
types of sclerenchyma
mechanical (nonconducting) sclerenchyma
sclereids
more or less isodiametric, often dead at maturity
conducting sclerenchyma( tracheary elements)
tracheids
long and narrow with tapered ends; contain no perfections.
dead at maturity found in all vascular plants.
vessel elements
short and wide end walls
dead at maturity
found almost exclusively in flowering plants.
external organization of stems
stem is an axis
Leaves are attached at nodes, and internodes, the regions between nodes.
phyllotaxy
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 with their nearest neighbors
Distichous: leaves located in two rows only
internal organization of stems: Arrangement of primary tissues
Epidermis
the outer surface of an herbaceous stem
barrier against invasion by bacteria
all interchange of material between a plant and its environment
cortex
interior to the epidermis
composed of photosynthetic parenchyma and sometimes collenchyma
some cortex cells contain large crystals of calcium oxalate or deposits of silica.
vascular tissues
phloem
Two types of conducting cells; sieve cells and sieve tube members
xylem
two types of cells; Tracheids and vessel elements
Stem Growth and Differentiation
Epical Meristem, Sub epical meristem,
