ASEXUAL SPORES. The diverse names given to asexual spores usually indicate some peculiar character of the spore or the group of plants which produce it. Among the green alga? (Chlo rophycete, q.v.) the characteristic spore is a zo ospore or swarm spore, a minute, pear-shaped naked mass of protoplasm, swimming freely by means of one or two cilia at one end (fig. 9). Among the brown algie q.v.) the zoospores are bean-shaped, with two cilia on the concave side. Among the red alga' (Rhodophy cete, q.v.) the spores have no cilia and hence can not swim, and as each sporangium produces four such spores they are called tetraspores.
Among the fungi, asexual spores, which are produced in great profusion and variety, have received many names. Among the alga-like fungi (Phycomycetes, q.v.) they are developed in one celled sporangia, and are mostly light, dry cells, easily scattered by wind. Such are called simply with no designating prefix. Among the sac-fungi (Ascomycetes, q.v.) , however, two con spicuous forms of asexual spores occur: the one, conidia, which are successively cut ofI from the tip of a filament, often forming chains; the other, ascospo•es ( fig. 4), developed within a delicate sac (asens). Among the rusts (Uredi nales, q.v.) the greatest variety of asexual
spores for one plant is reached; e.g. in wheat rust there are four. Among toadstools (Basidiomy cetes, q.v.) the characteristic spores are basidio spores, borne two or four together on the tips of pointed branches from a swollen filament, the basidium (fig. S). There are several other spores of minor significance among the fungi, each with its distinctive name. Among the bryophytes (liverworts and mosses) and most of the pterido phytes the asexual spores are called simply spores. In heterol)orous plants (some pterido phytes and all spermatophytes), however, there are two kinds of asexual spores, megaspores or macrospores and microspores (qq.v.). Before their character in seed plants was appreciated these two kinds were called respectively embryo-sacs and pollen-grains. In all of these wind-dispersed asexual spores, the spore-wall consists of two lay ers, a delicate inner one (intine or endospore) and a tough outer one (exine or exospore), often variously sculptured. especially in the pollen grains of flowering plants. and sometimes even winged, as in the pollen-grains of pines (fig. 2).