Glycine max (soybean) is the only angiosperm which is thought to exhibit somatic crossing-over. The variaties L65–1237 and T219 have gene combinations Y 11 Y 11 , Y 11 y 11 and y 11 y 11 resulting into dark green, light green and golden yellow leaves, respectively. The heterozygous plants are found to have dark green, yellow and double (dark green—yellow) spots on the two simple leaves and rarely the first compound leaf. The other two genotypes are usually devoid of spots. It has been suggested that the twin or double spots result from somatic crossing-over; (15) the single spots may originate from the failure of one or the other component of the double spots, from structural and numerical aberrations of chromosomes, and from point mutations. The idea that some sort of controlling element is causing the production of spots does not appear tenable. When seeds are treated with 3 H 2 O, the frequency of all types of spots increases. However, the relative proportions of spots remained comparable to those in the control over a concentration range of 5–100 μCi/ml. This indicates that the processes effected by β-particles from 3 H are similar to those effected by some sort of presumed internal mutagen produced during storage. The treatment of seeds with 50–750 R of γ-rays ( 60 Co emitted) increased the frequency of all types of spots, but yellows increased most in frequency followed by dark greens. This effect could be due to increased incidence of segmental losses, numerical inequalities and mutations of the gene Y 11 . The reverse, viz. the specific mutation of Y 11 →y 11 , would be very rare. The differences between the effects of two types of radiations may be due to differences in their relative biological effectiveness. The frequency of spots on the lower surface of the leaves is a fraction of that on the upper surface. Radiations used did not change this picture. It could be due to resistance of the spongy mesophyll to the mutagens applied or to differences in the developmental aspects of the two layers. The frequency of the specific locus (Y 11 ) mutations increased parallel to the frequency of total abnormalities, indicating that chromosomal processes are as vulnerable to the effects of radiations as the processes leading to the production of point mutations.