algae

Century Dictionary and Cyclopedia

1. A division of thallogenous chlorophyllous cryptogams found for the most part in the sea (seaweeds) or in fresh water. They are wholly cellular, though varying exceedingly in form and size, from a single microscopic or sometimes large and branching cell, a shapeless, jelly-like mass, or mere string of articulations, to forms with trunk-like stems and membranous laminæ many feet in length. Nourishment is absorbed by the surface of the plant, never through roots. The mode of propagation varies greatly in the different orders. In many no well-defined sexual differences have been discovered, and reproduction is carried on by means of cell-division or by non-sexual spores (tetraspores, zoöspores). In the highest order there are distinct male and female organs (antheridia and oögonia). The term Algæ as used by Linnæus and early botanists included not only seaweeds, but also the Hepaticæ, Lichenes, and Characeæ. By Harvey the Algæ were divided into three groups, distinguished chiefly by their color, viz.: the olive-brown, Melanospermeæ; the red or purple, Rhodospermeæ; and the green, Chlorospermeæ. This arrangement has now become nearly obsolete. Recent authorities have proposed several different schemes of classification for the thallophytes in general, in which structure and development, as well as supposed relationship, are taken into account, and in which the Algæ are variously distributed. Substantial agreement is not yet reached, and the nomenclature for many of the groups remains in a very unsettled condition. It may, however, be said that the Algæ are now generally divided into the following orders (classes, etc., of some), viz.: Florideæ, the most highly developed, producing cystocarps after fertilization; Oösporeæ, propagating sexually by oospores; Zoosporeæ, distinguished by the conjugation of zoospores; Conjugatæ, including the diatoms, desmids, etc., in which there is a conjugation of cells; and a remainder, the Cryptophyceæ of Thuret, variously disposed of by other authors, in which there is no known sexual reproduction. Many of the Algæ are edible and nutritious, as carrageen or Irish moss, dulse, laver, etc. Many abound in gelatin, and make a fine glue or substitute for isinglass. Kelp, iodine, and bromine are products of various species. Seaweeds are also valuable as fertilizers.

Wiktionary

1. n. Plural form of alga.

GNU Webster's 1913

1. n. plural of alga.

WordNet 3.0

1. n. primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves