PLASTIDS (front Gk. rNacr-r6s, plastos, mold ed, from z-Xciacretv, plasscin, to form) , or CHROMATO PROBES. Living organs of the cell, usually im bedded in the cytoplasm, of various form, having functions differing according to their ultimate mode of development. They differ from the nucleus in form and composition, and in multi plying by direct division. They are of three kinds—chloroplasts, chromoplasts, and leuco plasts. Chloroplasts (q.v.) contain chlorophyll and carotin, with often other subordinate pig ments which add their special tint to the general yellow-green of the ordinary chloroplast chro moplasts (q.v.) have usually a red or yellow color, due to a predominance of carotin: leuco plasts (q.v.) are colorless and have as their spe cial functions the formation of starch grains, proteid granules, or oil drops, out of material absorbed from the adjacent protoplasm. The oil
formers have been distinguished as elaioplasts. Multiplication of plastids by direct divison con sists in the severance of the protoplasmic matrix into two parts by its contraction, which con tinues near the middle until the two portions are completely disjoined. Plastids are minute and undifferentiated in embryos, and take on special form and character under the influence of the external conditions. Thus, plastids which de velop near the surface of the plant are likely to form chlorophyll and become chloroplasts: those which develop in subterranean organs or thick aerial parts are likely to become leucoplasts and act as starch or proteid formers; while the plas tids in flower leaves, the fruit, or even those in the root (e.g.. the carrot) may develop as chro moplasts. See CELL: MITOSIS.