Studies on the Number of Shoot Units with Crown Roots in a Stem of Rice Plant, in Relation to the Number of Leaves on It

Abstract

In relation to the number of leaves on a main stem or on a tiller of rice plant, the top shoot units with crown roots in a stem, in other words, the number of shoot units with crown roots from the bottom in it, were observed. The number of leaves ranging from 10 to 21 on a main stem and that from 4 to 10 on a tiller were obtained according to difference of varieties and/or growth conditions. The number of shoot units with crown roots in the main stem was in proportion as the number of leaves on it increased, with increase of the former of 0.68 in lower roots and 0.67 in upper roots for the increase in 1 of the leaves (Figs. 1 and 2). In more detail, however, the number of shoot units with crown roots increased stepwise with increase in the number of leaves (Figs. 1, 2 and Table 2). The number of shoot units without crown roots in the main stem was also proportional to the increase in the number of leaves on it, and increase per leaf was 0.32 in lower roots and 0.33 in upper roots (Figs. 3 and 4). As to the tiller, the number of shoot units with crown roots increased by about one with the increase in one leaf on it (Figs. 5 and 6), and the number of shoot units without crown roots coincided with that of the main stem in the same plant (Figs. 7 and 8). From these results, it is considered that a rice plant with a larger number of leaves on its main stem has older roots in its ripening stage, though it has more numerous shoot units with crown roots. For, it takes more time from the appearance of the crown roots in the top shoot unit to the fully ripened stage in such a plant, because of its plenty of shoot units without crown roots, which develop after all the shoot units with crown roots have appeared.