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Tissues and the Primary Growth of Stems (External Organization of Stems…
Tissues and the Primary Growth of Stems
External Organization of Stems
nodes, internodes, leaf axil, axillary bud, bud scales, terminal buds
phyllotaxy-arrangement of leaves
stem-axis, shoot-stem leaves & flowers
only a few buds develop branches
Internal Organization of Stems
Arrangement of Primary Tissues
Vascular Tissues
Xylem & Phloem
Plant is not circulatory
Xylem
tracheids & vessel elements
Helical, Scalariform, reticulate thickening
Vessels must absorb water
Cortex
Interior to epidermis
Secrete latex, mucilage, or pitch
Phloem
sieve cells, & sieve`tube members
Nuclei degenerate but remain alive
Epidermis
Outermost surface
Elongate outward become trichomes
guard cells and stomatal pores form stoma
Stomatal pores allow photosynthesis to occur
Vascular Bundles
Xylem and Phloem occur together
Bundles are collateral
Basic Types of Cells and Tissues
Collenchyma
Exhibits plasticity and ability to be deformed
Provides resistance to the parenchyma
Thick in the corners
Sclerenchyma
Revert back to original shape
Conducting and mechanical sclerenchyma
Cell walls are elastic
Develop by cell division
Parenchyma
Chlorenchyma, Grandular, and Transfer cells
Some die at maturity
Most common type of cell and tissue
Stem Growth and Differentiation
exterior cells mature as protophloem, interior become metaphloem
Rate of maturation varies species to species
Apical meristems and subapacial meristem
