CHARA'CEIE, aquatic plants, forming, according to some botanists, a distinct natural order of acotyledonous plants; according to others, a sub-order of algcr. Their stems are tubular, consisting either of a single tube, or of parallel tubes, a central one with smaller ones applied to its surface; they are either pellucid or incrusted with carbonate of lime, which is not to be regarded as a mere accidental incrustation, but belongs to their proper structure; and they have whorls of symmetrical tubular branches. They grow in stagnant waters, both fresh and salt, are always submersed, and often completely conceal muddy bottoms. A number of species arc natives of Britain, all belonging to the genus Mara. The organs of reproduction arc of two kinds—lateral globules, and axillary nucules. These organs have caused no little difficulty to botanists; the nature and use of the globules in particular being by no means well understood. The simple cellular structure of the C., apart from all consideration of their reproductive organs, associates them with the lower algre, rather than with phanerogamous plants. None of
them is of any known use. It was in the C. that the beautiful phenomena of cyclosis (q.v.) were first observed. Sir David Brewster discovered that each of the minute calcareous particles incrusting the C. possesses double refraction, and has regular neutral and depolarizing axes.
Fossil calcareous incrustation which covers the organs of repro duction, as well as the stems of some C., has, from its power of resisting decomposition, caused the abundant preservation of this order in the tertiary fresh-water strata. The nucules originally described under the name of gyrogonites, and supposed to be foram iniferous shells, have been noticed by E. Forbes in strata as old as the middle Purbeck beds. No remains of these have been observed in newer deposits, until we find them in the tertiaries. The nucules, associated with lymneea and planorbis, are very abun dant in the eocene Bembridge beds (q.v.).