Apogamy, apospory and parthenogenesis in the pteridophytes. II

Abstract

There can be no doubt that the plants most favorable for the study of apogamy and apospory are the homosporous leptosporangiate Filicales, in many of which these deviations in life cycles have been found to occur in nature and also under cultural conditions. They are not, however, at present fully understood. In a large number of ferns, apogamy is known to be a constant phenomenon, but apospory of this nature has been found in only a single fern, Scolopendrium vulgare. The discovery of its constant occurrence was made as a result of the studies of the inheritance of apospory in certain ferns by Andersson-Kott6 (1931, 1932) and Andersson-Kott6 and Gairdner (1936). Both apogamy and apospory are sometimes described as abnormalities in the life cycle of a plant. It is commonly assumed that if one of these phenomena occurs in a life cycle, it must be followed by the other one. However, it is known that only apogamy occurs in some ferns, and that apogamy is the only way in which the sporophyte is reproduced in those cases. In some apogamous ferns apospory may occur, but it may also be found in non-apogamous ones. It is suggested by the writer that both apospory and apogamy may be considered as normal phenomena in the life cycle, and are not necessarily related. For a brief discussion of the independence of these phases in a life cycle, the reader is referred to an earlier paper by the writer (1939). Studies of apogamy and apospory in the Pteridophytes during the decade just past (1939-1949) have not been niumerous. Hence this group of plants, so favorable for cytological study of these phenomena and others of a physiological nature, has interested comparatively few botanists. During the past ten years, however, a number of papers have appeared on various phases of apogamy and apospory as follows: