Abstract
The present paper is a report on the formation of first internode and beginning of internodal extention in rice shoots, and it also describes the varietal differences and ecological responses to the varying times of cultivation. Definitive nodes and internodes are here defined as those that are clearly delimited in longitudinal median sections of living shoots as observed using dissecting microscope. By these easy methods, the first discernible internordal lacunae are considered here as an index of internodal extension. From the results of this observation on the morphogenetic process, the author proposed that the stem development may be divided into the following three phases; viz. previous phase of internodal lacunae formation named "Primitive phase", process of subtle elongation of basel telescoped lacunae (Crown-internodes) named as "Primary phase", and the following phase showing the rapid and long extension of upper internodes (Culm-internodes) named as "Secondary phase". It is observed that the stage of first internodal formation in the Primary phase may correspond to time far previous to differentiation of panicle primordium. The plant-age as measured by the number of leaves is about 5.5. And in most plants, first extended internode is that between 5th and 6th node, however, the locus of this node keeps lower in short-term varieties and in plants planted late, but upper in long-term varieties and in early planted plants. The number of extended internodes in Primary phase may be found 5 or 6 in most plants, and are less in short term varieties but more in long-term varieties. However, ecological variations due to the varying of planting times are a little. These internodes are 1-2 mm in length at the beginning of formation, and are extended just about 3 mm in full length. And the internodes which are extended over 3 mm in length may be regarded as the internodes of Secondary phase. At the stage of onset in Secondary phase, the panicle is 0.4∼1.0 mm in length, and the stage ranges from the branch differentiation to early time of spikelet formation. And the plantage is 11.0∼14.0 leaves, leaf number index is 83 to 87, and the Secondary extension of internode begins from the node of 10∼13th leaf. Each above-mentioned value is revealing the range of varietal differences. It seems that the "crown" of Grasses may be divided into two types with or without of "crown-internode"-Rice-type crown (with) and Wheat-type crown (without). From the results of this studies, the author stated that the simple method using dissecting microscope may be useful for identifying the internodal formation and extension not only at the Secondary phase but also at the Primary phase, without any trouble as by paraffin method.
