Cultivated Rice Varieties viewed from Root Characters : (III) Ferrous coatings in root

Nine rice varieties including three root types (I, II and III) were grown in both a nursery and a paddy field without transplanting. From both conditions samples were taken at their yellow maturation stages, in order to determine root ferrous coatings. The determinations were made by the o-phenanthroline method, after coatings were washed away by boiling the roots in IN-HCl for 45 minutes. From these experiments, it was found that the varieties belonging to the type I, of which root weight were larger than those of type II and III, were apt to have larger coatings per both plant and root (Fig. 1 & 2). As to ferrous coatings per unit surface area, it was nearly the same as those above mentioned (Fig. 3). Root surface area was calculated from root weight by such a formulae as A≒√^3(W proposed by the authors, in which A is the surface area and W is the weight per root. In addition to these experiments, seasonal changes of ferrous coatings were determined every 16 days after sowing, using three varieties of each root type. From these, it was found that, (1) ferrous coatings per unit surface area showed their maximum 44-60 days after seeding respectively according to varieties and then are gradually reduced till the period from heading to maturation (Fig. 6) and (2) those per plant and per root increased with the growth up to the maximum found at heading time (Fig. 4 & 5). These changes in coatings were also contrasted with the changes in the relative growth rates calculated by root weight increase. Maximum values in coatings were always observed at the periods when the growth rate dropped, that is, when the root activity lowered (Fig. 4, 5, 6 & 7).