Algæ (alje)

pl. [L., pl. of alga: see alga.] 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 IMG:content-0486.png:[blocks in formation] cell, a shapele , jelly h like ma , or mere string of articulations, to forms with trunk like stems and membranous lam inæ many feet in length. Nour ishment is absorbed by the surface of the plant, never through roots. The mode of propaga tion 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 Characee. By Harvey the Algæ were their color, viz.: olive-brown, Melanos per meæ; in teg roups, distinguished chiefly by or purple, Rhodospermeæ; and the green, Chlorospermeæ. This arrangement has now become nearly obsolete. Recent authorities have proposed several different schemes of cla ification 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 (cla es, etc., of some), viz.: Florideæ, the most highly developed, producing cystocarps after fertili. zati on; Oosporeæ, propagating sexually oöspores; Zoö sporeæ, distinguished by the conjugation of zoöspores; Con jug atæ, including the diatoms, desmids, etc., in which there is a conjugation of cells; and a remainder, the Cryp tophyceæ 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 mo , dulse, laver, etc. Many abound in gelatin, and make a fine glue or substitute for isingla . Kelp, iodine, and IMG:content-0487.png:[blocks in formation]