Characteristics of the Rice Plant with the Modified Flag Leaf from the First Bract

Abstract

There is a contradictory point of view against Matsushima's diagnoses concerning the rice plant of which first bract was modified to the flag leaf. Therefore, the characteristics of the rice plant with the modified flag leaf were investigated. Three types were observed in the morphology of the neck node. The first type developed one or no primary rachis-branch and formed complete annular protuberance around the whole circumference of the neck node. This type is usually seen and is considered as a normal one. The second type had incomplete annular protuberance around the neck node and contained two subtypes. One resembled the normal type but a part of the circumference of the neck node was lacking in protuberance (Fig.1, A). The other had two or three primary rachis-branches on the neck node and a part of its circumference was lacking in protuberance (Fig. 1, B). The third type had twin or triplet whorled primary rachis-branches and had complete annular protuberance around the neck node (Fig. 1, G and D). The rice plant having a normal neck node did not possess a car or a bud in the axil of the flag leaf except for one which had a bud (Table 1). And the bud was true one of a tiller. Many plants with the other two types of neck nodes carried the axillary car or bud at the flag leaf (Tables 1, 2 and Fig. 2, A, B and C), though there were also a lot of plants having none (Tables 1 and 2). The morphology of the ear was as follows. A prophyll was absent (Fig. 3, A). Earlets were formed alternately on the two linear planes of the axis of the ear (Fig. 3, E). 0ne or two basal earlets had a bract-like structure, some of which were developed well (Fig. 3, E). One or two basal earlets had a bract-like structure, some of which were developed well (Fig. 2, B and Fig. 3, B). But it was bladeless (Fig. 3, B) and did not encircle the axis of the ear (Fig. 3, C and D). The axis of the ear was not hollow and showed a typical feature of an atactostele in the transverse section (Fig. 4, A). The number of large vascular bundles in the axis were two and almost one in the second internode and in the third one respectively, regardless of the number of diverged earlets (Table 3 and Fig. 4, A, B and C). The morphology of thirty-nine buds out of forty-three subtended by flag leaves of the rice plants with the second type or the third of the neck node was the undeveloped feature of the ear mentioned above. But about the remaining four, it was undistinguishable whether they were the buds of the ear or of a tiller, for they had only a leaf-primordium-like structure in which none was contained. The lowest elongated internode of the stem was longer or the number of elongated internodes was more by one in the rice plant of which neck node type was the second or the third, when compared with that of the first type (Table 4). From these results, it is considered that the ear in the axil of the flag leaf and the bud of which morphology was the undeveloped ear are not a tiller but a primary rachis-branch. Therefore, such the flag leaf as this is the one to which the first bract has been modified. And this results in the conclusion that the second type of the neck node morphology and the third one are the characteristic expression of the rice plant with the modified flog leaf from the first bract. Then, the problem still remains about rice plants which had undistinguishable buds or none in the axil of their flag leaves, although their neck node morphology was the second or the third type. But, as their feature of the stem internode elongation differed from the rice plant with he normal neck node and was the same as the one of which first bract had definitely been modified, those plants are also the rice plants of their first bract having been modified. [the rest omitted]