Abstract
The interrelationships among quantitative elements of the rice root system were discussed in two varieties, chiefly the relations between primary rots, root surface area and others. Number of primary roots must be the main factor which determines the whole development of the root system. The development of the root system must be ascribed to the extension of the root surface area, which may bring roots into contact with soil particles, nutritive elements and water molecules, so as to make the uptake increase. It was made clear that number of primary roots were significantly correlated with number of secondery roots, total length, total dry weights and the whole surface area of roots (Fig. 1. A∼F) (Fig. 2. A∼F). In addition, the whole surface area went hand in hand closely with number of lateral roots, total length and total dry weights of roots (Fig. 3, 4. A∼D). From these facts, the authors, were able to estimate the whole surface area from the regressions between the area and other quanta. For example, two formulae, such as log A=0.763+0.877 log W and log A=0.243+1.066 log W, were derived for the 11th and 3rd leaf stages respectively. High correlations were, moreover, ascertained between the presumable real surface area and the values calculated from those formulae, such as above mentioned and the theoretical one (A=N1/3×W2/8), which was already proposed by the. author (1959) (Fig. 5, 6). Rot diameter was not always correlated with those quanta of roots mentioned above. Rot diameter was rather dependent upon the develpment of the constituting tissues, such as cortical layers and stele system (Fig. 7, A∼F). Cortical layers originate lysigeous cavities which concern with the oxygen supply from top to root and the stele system relates to the migrations of the nutrients and water absorbed. Thus root diameter must regulate the physiological activity in roots, inclusive of the whole plant. Among four varieties of which the resistabilities against soil reduction were known, the relation between the resistability and root tissue development was examined. It was in general clarified that the more resistant the variety was, the larger the development of those tissues were (Fig. 8).
