Cyto-histological observations were carried out on the morphogenetically abnormal rice spikelets caused by a low temperature, 14∼18°C. Several cyto-histological abnormalities were found on the stamens, such as, unusually swelled anthers with stigmatic pieces, loculi with tapetal hypertrophy, plasmodium-like matters and abortive pollens etc., as seen in figs. 1∼3. The complex types of various kinds of abnormalities as seen in figs. 2, 3 and 6 were found frequently, suggesting that these abnormalities not were independent each other, but were caused fundamentally by a common physiological background of feminization. On the female organ, various grades of additional ovary formation from carpel-like structures to ovaries as seen in figs. 16∼25, were observed and a good many of the varied multi-pistils and the pistils with multi-ovaries were found in the spikelets consequently. In general, these tendencies of feminization has been said to be brought about by the level-up of the endogenous auxin content. From the fact that the morphological and cyto-histological abnormalities due to the low temperature are quite similar to those induced by the application of gibberellin, it is considered that the gibberellin-like substances may have some strong connection with the spikelet morphogenesis under the low temperature and may act to promote the feminization effects of auxin at the later stage of spikelet formation. About the outgrowth phenomena of the unknown tissues from the ovaries, they were clarified to be resulted from the followings, these were, the unusual development of integuments-particularly the outer one as shown in figs. 8∼11, the disclosure of ovule itself as shown in figs. 12 and 13, and the continuous growth of a part of the fasciated portion of two ovaries as shown in figs. 14 and 15 etc., seemingly due to the so-called "flower vegetativation". Occasionally, the vessel-like cells with partially thickened cell wall as seen in fig. 26 were found at the undeveloped embryo sac mother cell or tetrads and some their neighboring cells. Not only the irregular arrangement of egg cell, synergids, antipodes and polar nuclei in the embryo sac but also abnormal enlargement or degeneration of them, as seen in figs. 27 and 28, were also observed frequently. It was indicated that the sexually intermediate structures changed from stamens appeared most repeatedly on the stamens initiated at the palea side, above all on the right or left one which has developed at the most proximity of the female organ.
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