| Abstract: | Summary On the dioecism in idesia polycarpa maxim. Idesia polycarpa Maxim. is a dioecious species, native of Japan and China. Two specimens have been studied for this research, a ♀ and a ♂ one, growing in the Botanical garden of Siena. The female plant does not present anomalies in the sex behaviour; the male plant, on the contrary, bears occasionaly some flowers with ovaries, which exceptionally develop into fruits. In the Botanical Garden of Pisa a case of complete sex inversion has been observed (male into female). In both the ♀ and the ♂ the first development stage is identical and hermaphrodyte. The flower is tendentially proterandrous, unisexuality being attained only successively. In the male flowers the pystil degenerates while the pollen mother cells undergo meiosis. The ovary ceases developing farther, at the ovule forming stage from the placentae. The only cellular line which degenerates is the epithelium, which lines the ovary inner surface and extends as far the upper surface of the stygma. The microspores tetrads form contemporarily. The tapetum is of the secretory type. The stamens degenerates in female flowers at the moment corresponding to the passage from the vegetative to the reproductive stage; i. e. the stamens of the female flowers are not capable to carry out the meiosis. The first cellular layer to be reached by a degeneration process is the tapetum; the second is the archesporial tissue. During the degeneration of these two tissues ovules are developing. The female gamethophyte is of the monomegasporial, normal, eightnucleate type. The fruits born by the female plant are roundish, with 8–30 fertile seeds and 50–65 sterile ones. Thè fruits which are exceptionally born by the male plant are bigger, pear-shaped, and countain 20–40 fertile seeds and 65–85 sterile ones. The epithelium lining the ovaries undergoes total degeneration in normal male flowers; a partial one in the occasional male flowers which have more or less developed pistils. When only the stygma epithelium degenerates, the ovary produces a higher number of ovules even through the whole style region, so that a style does not form and the ovary does not shut, giving a pear-haped fruit. A higher number of seeds are therefore produced by such an ovary, not only because the placentae go on producing ovules for a longer period, but because also their stylar region is active in this process. It is evident then, that the stigma plays a very important role in the normal closing of the ovary. In the cases of partial degeneration, ovules remain vital only where the corresponding epithelium is unaltered. This shows that the epithelium has a great importance in the ovule producing phase of the placentae. Everything seems to point out that the anthers degeneration is autonomous, owing to its own incapacity to undergo meiosis. On the contrary the suppression of the ovary in the male flower is not autonomous and does not occur in a particular moment of the ovary development, but it coincides with microsporogenesis. The suppressor of the ♀ sex therefore acts through the opposite sex. In a male plant where the anthers happen to degenerate, pystils develop in various degree, even completely. The flowers of the female plant reache the microsporogenesis stadium about 15 days later than those of the male. The author suggests that this delay may be responsible for the realization of the female sex, checking the normal development of the anthers, probably under the influence of environmental factors. On this base he has tried to explain anomalies in male flowers. |
