ARCHEGONIUM, fir'1:6-g5'ni-fint (Gk. dp arehegonos, first of a race, primal). 'rice peculiar female organ of mosses, ferns, coni fers, etc.. which together are often spoken of as Archegoniates. It is a flask-shaped organ, consisting of a neck more or less elongated and a renter more or less bulbous. A single egg occupies the venter, and in the process of fer tilization the sperm enters by the open neck of the archegonium and conies in contact with the egg. Among the mosses the archegonium is a free and often stalked organ. Among the liver worts the archegonia are variously disposed on the thallus-body, while in mosses they are borne in a cluster at the apex of the leafy shoot or of its branches, the terminal rosette of more or less modified leaves forming what is often called a 'moss flower.' Among the ferns the archegonia are usually borne upon the under side of the in conspicuous sexual plant (prothallium), the ven ters being imbedded in the tissue and the necks more or less projecting. In the water ferns, quillworts, and little elub-mosses, the female plant is developed as a tissue within the spore. whose heavy wall breaks or cracks at a certain place, and in the exposed part of the female plant the archegonia are developed. Among the conifers the spore, with its contained female plant, is retained within the ovule, and hence the archegonia are not exposed. but lie im bedded in the superficial part of the female plant (endosperm), toward the mieropyle (the pas sageway left by the integument). Among the conifers the male cells are brought to the arche gonium by growing pollen-tubes. The pollen grain, containing the male cells, rests at the base of the micropyle, upon the apex of the nucellus (central part of the ovule). The tube
penetrates the tissue of the nucellus and reaches the embryo-sac (megaspore), just within which are the arehegonium necks. It then pierces the sae-wall, enters and crashes the neck, and dis charges its male cells into the egg.
Among the flowering plants no archegonia are developed, the embryo-sae containing a free egg. along with other free cells of a much-reduced female plant.
The development of an arehegonium and its preparation for fertilization are matters of great morphological interest. It begins as a single superficial cell of the sexual plant. By repeated cell divisions the layer of cells constituting the neck and venter is formed, and this surrounds a single row of axial cells. The cells of this row (variable in number) which lie within the neck are called the "neck canal cells," while the lowest cell of the row, the one within the venter, forms the egg. When the archegonium. is nearly mature the row of neck canal cells breaks down and leaves an open neck: and usually just before fertilization the cell in the venter cuts off a small cell toward the neck called the "ventral canal cell," which rapidly disorganizes and leaves the egg free and alone in the venter. ready for the approach of the sperms through the neck.
One of the interesting facts in connection with archegonia is that the apical neck cells secrete a substance which attracts the sperms toward them. For example, this substance is not the same in mosses and ferns. so that even if arche gonia of the two groups are close together the moss sperms and the fern sperms will be at tracted only to their own archegonia.