AN'THERID'IUM (a diminutive after the Greek fashion from anther; see ANTHER ) . The male organ of plants; that is, the organ in which the sperms are developed. Among the algae and fungi an antheridium is usually a single cell, and in the simplest forms in which antheridia appear this single cell is merely a nutritive cell which is used for the purpose of producing sperms. In most algae and fungi, however, the antheridium is a distinctly differentiated cell set apart from the very first for the production of sperms. Among the mosses and ferns the antheridimn is a many-celled organ of varying shape. The moss antheridimn is a free organ and more or less club-shaped, a section showing that the wall con sists of a single layer of sterile cells, and that the rest of the structure is a compact mass of very small cells, within each one of which a sin gle sperm is organized. The antheridium springs open or bursts open in the presence of moisture and discharges its mass of cells and sperms, the latter of which free themselves by their movements and are ready to swim to the female organs. Among the ordinary ferns the antheridium is an imbedded organ, which dis charges its sperms in one way or another at the surface of the prothallium, With the introduction of heterospory (q.v.),
which involves certain of the fern-plants and all of the seed-plants, the male plant is very much reduced in size, being entirely contained within the spore that produces it, which in the seed plants is called the pollen grain. With this rednetion of the male plant, the antheridium is correspondingly nn)dified, so that it is a matter of discussion in such cases as to just what cell or cells may represent an antheridium. The or gan, therefore, in the seed-plants does not stanch cut with the distinctness that it presents in the three lower groups, but it is none the less repre sented.
The name is an unfortunate one, since it means "anther-like," having been given under the im pression that the anther of seed-plants is a male organ. It would be very desirable to change the name if such a thing were possible, and "sperm ary" has been proposed as a substitute.