Abstract
The authors tried to determine root types, using 280 cultivated rice varieties continuously grown in nursery. Nursery conditions favoured to make varietal defferences of root characters clearer than paddy field conditions. Three root types such as I, II and III were proposed by combining both root diameter and colour (Fig. 1). 1) From type I to III, roots became thinner and paler in colour (Tab. 1 & Fig. 8). Shoots also went hand in hand with root types, showing poorer growth in height and weight (Fig. 3 & Fig. 4). But thinner root types had larger ears in weight in contrast with culms (Fig. 5). Thicker types showed leaf tip burn earlier than thinner ones and showed also lower promotion of premature heading in nursery (Fig. 6 & Tab. 5). From these, root types suggested different abilities of physiological function. 2) Majority of varieties cultivated in temperate zone of Asia belonged to type II and III, but local varieties in Japan, "Hsien" in China and tropical ones included large numbers of type I (Fig. 2). 3) Among those varieties including type II and III which had different resistabilities against soil reduction, there were also differences of root diameter. The more resistant the variety, the larger the root diameter (Tab. 7). More resistant ones were, moreover, capable to produce larger numbers of roots and longer ones, even in solutions which were made reductive by adding hydroquinons (Tab. 8). These facts explained their resistabilities from morphological viewpoints as well as from physiological points already studied by many investigators.
