Abstract
Some morphological observations were carried out on the proliferations in the mutant spikelets induced by X-ray irradiation in Oryza sativa L. var. Reimei. X-ray was irradiated on seeds at the dosage of 20 kR. in 1966, followed by sowing in soil. Spikelets which were used for observation had been sampled in the year from 1968 to 1972. Results which have been obtained were as follows; 1) One or more spikelet-like organs were found in the spikelet. 2) One or more leafy-shoots which have been composed of many leaf-like glumes were found in the spilelet, the tips of which had (a) one or more spikelet-like organs, (b) incomplete ovary, (c) stigma-like intermediate organs having no ovarian structure, or (d) vegetative shoot having no reproductive organ. There were general tendencies in those spikelets having proliferations mentioned above, such as (1) rudimentary glume had no change, (2) lemma and palea had many veins in themselves exhibiting slender forms, (3) the position of spikelet-like organs to differentiate was above that of palea where reproductive organs differentiated usually, and no reproductive organ was found in that place. It was considered that these spikelet-like organs or leafy shoots were the typical proliferations, and those proliferations would have been induced just before the time of differentiation of reproductive organs on the apical meristem of spikelet primordium, and that those proliferations might be initiated as the result of the supression of transformation of apical meristem from vegetative stage to reproductive stage in a narrow sense. Judging from the results and considerations mentioned above, it was presumed that the apical meristem of the spikelet primordium which was going to differentiate proliferation maintained relatively larger size and more differentiated organization than those of the control at the time when stamen primordia differentiated. Some discussions were undertaken on the physiological and genetical background of the development of the proliferations.
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