Ergastic substance
Ergastic substances are non-
protoplasm materials found in
cells. The living protoplasm of a cell is sometimes called the
bioplasm and distinct from the ergastic substances of the cell. The latter are usually organic or inorganic substances that are products of metabolism, and include crystals, oil drops, gums, tannins, resins and other compounds that can aid the organism in defense, maintenance of cellular structure, or just substance storage. During the lifetime of a cell, these can appear and disappear, indicating some level of participation in life processes. Ergastic substances may appear in the
protoplasm, in
vacuoles, or in the
cell wall.
Cellulose and
starch are the main ergastic substances of plant cells. Cellulose is the chief component of the cell wall, and starch occurs as a reserve material in the protoplasm.
Starch, as
starch grains arise almost exclusively in
plastids, especially
leucoplasts and
amyloplasts.
Although
proteins are the main component of living protoplasm, proteins can occur as inactive, ergastic bodies—in an amorphous or crystalline (or crystalloid) form. A well-known amorphous ergastic protein is
gluten.
Fats (
lipids) and oils are widely distributed in plant tissues. Substances related to fats: waxes, suberin, and cutin occur as protective layers in or on the cell wall.
Animals eliminate excess inorganic materials; plants mostly deposit such material in their tissues. Such
mineral matter is mostly salts of
calcium and anhydrides of
silica.
*
Raphides are a type of elongated crystalline form of calcium oxalate aggregated in bundles within a plant cell. Because of the needle-like form, large numbers in the tissue of, say, a leaf can render the leaf unpalatable to herbivores (see
Dieffenbachia and
taro).
