Studies on Root System Formation in Leguminous Crop Plants : 1. Three types of root system formation in main roots

[摘要] In the researches conducted so far on the formation of the root system of leguminous plants, stress has been placed, in most cases, on the study of how the roots spread underground. Consequently, the characteristics of root systems have been defined by a mere term of "the shallow-root type" or "the deep-root type." This study is different from the previous researches. That is, the study attaches importance not so much to the spreading condition of the root system as to the clarification of the characteristics observed in the developing process of branch roots. The purpose of the study is thus to find out a law of nature governing the growth of the root system, and, on this basis, to classify the root system in a new way. The experiment was conducted during the period from the autumn of 1960 to the summer of 1963. The varieties used in the experiment were as follows: Alfalfa (Atlantic) Common vetch Red clover Broad bean Ladino clover Chinese milk vetch Egyptian clover Soy bean (Hogyoku) Sweet clover Lupine (Yellow flower) Cowpea The results obtained were as follows: 1) As for the root system formation, it was observed that the main root began to grow first, and then branches of the first order started to grow from its base and extended toward the root apex (see Fig. 1). This phenomenon is common to all the specimen plants. 2) It was made clear that, as the plants grew, their root systems transformed from the uniform standard type to the following three different types according to their varieties: a. Alfalfa type b. Vetch type c. Intermediate type 3) Alfalfa type Fig. 2 is a schematic diagram showing the process of this type of root system. The main root (0) grows first, and the first-order branches (a1, a2, ……a8) appears from its base and extend toward the root apex one after another (Standard type). But subsequently, the second group of first-order branches (b1, b2, ……b6) begin to develop. Following their development, te subsequent groups of (c1, c2, ……c4) and (d1, d2) begin to take shape. This process of development is repeated at regular intervals. a) In the case of alfalfa, the development of first-order branches took place 4 to 5 times by the time when the plant began to blossom. b) The type of characteristics observed during the development of first-order branches were observable also in the case of branches of the second and third orders. c) It was interesting to note that the primodium of the subsequent first-order branches (such as b1, c1 and d1) appeared, as a rule, side by side with the initial branches (a). d) These characteristics were observed in the case of alfalfe, Chinese milk vetch, red clover, ladino clover and the like. e) These characteristics were not affected by soil conditions or reaping methods. 4. Vetch type This type of plant is far simpler than the alfalfa type in characteristics. That is, once first-order branches grow at the base of the main root and extend the root apex, no similar branches appear any more. Common vetches belonging to vicia group, broad beans and cowpeas presented this phenomenon. (See Fig. 4) 5. Intermediate type This type can be regarded as standing halfway between the alfalfa and vetch types. It is also conceivable, however, that this type originally belongs to the alfalfa or vetch type but none the less presents the characteristics peculiar to the "intermediate type" depending on the conditions surrounding the roots. In the author's experiment, soy beans and yellow lupines presented such characteristics.

[学科分类] 农业科学（综合）