Studies on the Mechanism of Leaf Formation in Crop Plants : II. Anatomy of the Lamina Joint in Rice Plant

Studies were performed on the nature of the curvature of laminae to the abaxial side in rice leaves, shown when they have almost accomplished their longitudinal growth. When the excised leaves from adult rice plants, were placed in a horizontal position being floated on distilled water, the angles between the laminae and the sheaths in the excised leaves, each consisting of 1cm of lamina, a lamina joint and 2cm of sheath, increased, becoming larger than those in the terminal leaves, held in a vertical position, intact on the plants (Tables 1 and 2). Thus the fact that the lamina joint is a main region to percieve and respond to geotropic stimulus was proved (Table 2). Such an increment in the angle was derived from that in the cell size in the adaxial side of lamina joint (Table 3). Moreover, the behaviour of the vascular system and the following mechanical structure in the lamina joints of healthy leaves and of tubular leaves, the latters being induced by 2, 4-D treatment, were histologically investigated. It was observed that these regions were liable to bend because their vascular bundles were transferred inwards and lignin in their mechanical systems disappeared. The lamina joint is also a transitional region between the lamina, having no dorsiventrality, and the sheath, having dorsiventral structure with reference to the arrangement of vascular bundles and ground tissues. No essential difference in such vascular system was observed between the healthy leaves and the tubular ones (Photos. 1∼16)