Collenchyma - found just below the epidermis in petiole (e.g. celery stalks), leaves, and young stems; usually specialized; characteristics include:
living at maturity
irregularly thickened cell walls (+cellulose)
prism shaped
plastic (can change shape but do not usually return to the original shape; remain deformed)
Functions of
collenchyma cells
include:
support
some involvement in transport of nutrients
Sclerenchyma - in mature parts of the plant, especially in woody plants and herbaceous perennials; specialized; characteristics include:
dead at maturity - protoplast is absent
very thick, sclerified cell wall (+lignin)
impermeable to water and other nutrients
in cells specialized for transport of water and nutrients, the cell wall contains holes called pits.
Functions include:
support
protection
transport of water and nutrients
Specific examples of
sclerenchyma cells
:
fibers - long and slender
sclerids (stone cells) - relatively spherical; the gritty texture of pears is due to the presence of stone cells.
