Majority of species of Riccia are homothallic like Riccia glauca. In this case, antheridia and archegonia are borne on same thallus. Heterothallic species like Riccia himalayensis are also common. In such species, antheridia and archegonia develop separately on different thalli. The sex organs are produced in the groove on dorsal surface of mature gametophyte.
Development of antheridium: The antheridium develops from a superficial dorsal cell called antheridial initials. It soon divides. It gives rise to two cells, upper one is called outer cell and the lower one the basal. Outer cell projects outside the thallus and the basal cell embedded in the thallus. It develops into embedded portion of stalk of antheridium. The outer cell develops into main antheridium. Outer cell further divides by transverse septa. It forms a vertical file of three cells: Two upper cells are called primary antheridial cells and they produce proper antheridium. The lowermost cell of file is called primary stalk cell. It produces projecting portion of stalk. Now, the two primary antheridial cells divide by two successive vertical division. These divisions are at right angles. As a result, eight cells are formed. These are arranged in two tiers and each tier consist of four cells. Now each tier of four cells divides periclinally. Thus each tier has four jacket initials and these jacket initials encircle four androgonial cells of each tier. In this way, in both tiers, eight primary androgonial cells are formed and these cells are encircled by eight jacket sterile initials. The sterile jacket initials repeatedly divide anticlinally. They give rise to a single layered jacket around the antheridium. Eight primary androgonial cells divide repeatedly. They give rise to a large number of cubical androgonial cells. Further divisions occur in these androgonial cells. As a result they become smaller and smaller. The last cell generation of androgonial mother cells becomes androcyte mother cells. Each androcyte mother cell divides diagonally. Thus each gives rise to two androcytes.
Formation of antherozoid from androcyte: Androcytes are soon metamorphosed into antherozoid. The process of metamorphosis is as follows:
Androcytes are triangular in shape with a big prominent nucleus. An extra nuclear granule, blepharoplast appears in the cell. The granule becomes large in size and adheres to plasma membrane. Very soon two flagella arise from the anterior end of blepharoplast. The androcyte becomes rounded. Nucleus becomes crescent shaped. It is shifted towards the blepharoplast and unites with it firmly. Thus androcytes are changed into antherozoids. During this process, the internal cell wall of jacket layer of antheridium disintegrate. It produces a liquid substance. Antherozoids lie in non motile condition in this liquid.
The main body of a mature antherozoid mainly consist of nucleus. The elongated blepharoplast adhered to nucleus. It bears two flagella at its anterior end. These flagella are used for movement in water. One flagellum of antherozoid helps in propulsion. The other helps in rotating the body. Sometimes, small unused portion of cytoplasm form vesicle. This vesicle remains attached to posterior end of antherozoid. The mature antheridium remains embedded in antheridial chamber. This chamber opens by an ostiole on the dorsal side of thallus. The mature antheridium consists of a few celled stalk and antheridium proper. The antheridium proper may be rounded or pointed at its apical end. A sterile single layered jacket layer encircles the antheridium and protects it. The mature antheridium contains androcytes within jacket layer. Each androcyte metamorphoses into an antherozoid.
The jacket layer of fully developed antheridium is gelatinous. It imbibes water. Thus antherozoids become gelatinized mass within antheridium. The antherozoids lie free in antheridium. They are embedded in viscous substance. Liberation of antherozoids from antheridium takes place by explosive mechanism.
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