A few investigators have hitherto reported that they succeeded to increase mutability of plants by keeping them under an abnormal condition of nutrition excluding a special chemical element, such as nitrogen, phosphorus or sulphur. Recently, the chemical analysis proved phosphoric acid was one of the essential components of nucleic acid, which was believed to be an heritable substance. Therefore, the effect of phosphorus shortage on the composition of nucl.eic acid, and consequently induction of mutation was examined in the present experiment. Progeny test of the lines of rice plants; originated from the seeds of plants which were cultured in nutrient solution wanting in phosphorus for whole the life except a few weeks at the seedling stage have progressed in these several years and a good number of variations, such as chlorophyl defect, poor growing habit, gigas-type, sterility etc., was found, but most of them were mere modifications and disappeared in the later generations.