Cyclic Manifestation of Sterility in Brassica pekinensis and B. chinensis

Abstract

The transition from asexual or vegetative growth to the condition of flower and fruit production in hermaphrodite plants is to be recognized as a most fundamental aspect of sexuality. Furthermore, the inter-relations that exist between vegetative and reproductive vigor and the influence of the former on the latter are reflected and exhibited in certain phenomena of sterility. It is now certain that vegetative vigor and the internal interrelations incident to it may limit reproductive vigor and sexuality. The limitation from these causes may take place in two ways: (i) they may interfere with or influence the morphological development of flowers or other reproductive organs, and (2) they may affect the functioning powers of organs that are fully formed. If these influences are marked, one or more types of sterility may appear. Only recently observations have indicated that, at least in some cases, the compatibilities and the fertility of the sex organs may vary rather definitely within the cycle of vegetative and reproductive development characteristic of the particular species. A phenomenon of this sort is reported by EAST and PARK (4), who found that in the few plants which are self-compatible in certain species and hybrids of Nicotiana, the self-compatibility develops only at the end of the flowering period. Cases of crosscompatibility appearing only at the end of the period of bloom are reported also. A very decided case of the development of selfcompatibility only at the close of the period of bloom was observed by the writer, in a plant of Lythrum Salicaria, and reported at the annual meeting of the Botanical Society of America for I9I7. These observations suggested that new evidence on the old problem of the relation between vegetative vigor and reproductive vigor, as expressed in the formation of flowers and the functioning of the