Abstract
Differences of the rice varieties, Norin-No.1, Yutaka-senbon and Haruta-Asahi in the developmental of the shoot apex during the growth of the plants were examined. The results obtined are summarised as follows : Definite varietal differences were observed among the three varieties in the period during which the increase of the number of cells in the shoot apex surpassed its width enlargement. The decline in the increase of the number of cells in proportion to the enlargement of the width in Haruta-Asahi took place earlier than in the other varieties ; it began after the leaves in the early tillering stage were initiated on the shoot apex, and continued till the reproductive leaf (leaf No. 12) appeared on the apex. This variety had not so many tillers as the others. Though the period in which the number of cells was higher in proportion to the width in Yutaka-senbon was longer than that of Haruta. Asahi, this proportion declined as the reproductive leaf (leaf No. 12) appeared on the shoot apex. This variety had comparatively rich tillers, the tillers in its late tillering stage, however, becoming invalid. The high proportion of the number of cells to the width in Norin-No.1 were maintained for some time after the reproductive leaf (leaf No. 9) appeared on the shoot apex. This variety tillered ever in the earlier stage of the differentiation of the young ear primordia and the percentage of the available tillers was higher than in Yutaka-senbon. Judging from the results mentioned above, it is certain that there are varietal differences in the changes of the shoot apex during the growth of the rice plant, and that there is a close relation between those differences and those in the external properties of the variety.
