Mechanism on the Development of Deformed Spikelets in Oryza sativa L. : III. The main vascular course and the morphological nature of the compound 2-flowered spikelet

[摘要] In order to make clear the morphological nature of the 'compound 2-flowered' spikelet [Plate 1-1, 2] in Oryza sativa L., the present investigations were carried out from two aspects as follows; 1) Gross morphological ones of the acropetal orders of each bract (glume and lemma) on its own spikelet axis and those of the disposed direction of each bract relative to the primary (or secondary) rachis in the inflorescence. 2) Anatomical ones of the vascular courses of the 'compound 2-flowered' spikelet with two ovaries. As a result of the first investigation, a concept was composed, which is to be called 'isobract'. This concept is defined as a 'set' of the bracts among which each acropetal order is equal on spikelet axis and each disposed direction is equal or bisymmetric relative to primary (or secondary) rachis. For example, in Plate 1-8, there are five isobracts; (rg1, I), (rg2, II), (eg1, III), (eg2, IV), and (1, V) respectively. The palea (p) and the bract VI aren't isobract because of the fact that the former is the bracteole on floret akis. Hence it is considered that the development of the bract VI is caused by the prolification of spikelet primodium and not by the reversion of phylogenetically degenerated bract. As regards this problem, other authers' interpretations arc discussed, particularly those of Parodi (1941) and Schweickerdt et al (1956). In the other side, it became clear from the second investigation that two main vascular bundles of floret axis exist in the stalk of the 'compound 2-flowered' spikelet. One diverges from mother vascular bundle at the axil of the bract V and the other does in the same manner at the axil of the bract VI [Plate 2, vfa and vfa']. The mode of the vascular courses, where each main vascular bundle of floret axis diverges from that of spikelet one (mother vascular bundle), is plainly the same as that of the normal spikelet. These results demonstrate that the stalk of the deformed spikelet consists of three axes; one spikelet axis and two floret ones, the letters independently arise at each axil of the bract V and VI, and have grown together in each dorsal side. Therefore the 'compound 2-flowered' spikelet with two ovaries truly had two florets which has compounded ontogenetically. The hypothesis and Model II (Matuba, 1971) mentioned in previous report are thus confirmed.

[学科分类] 农业科学（综合）