2. Dull endosperm, du, which intensifies suam and su1 (see Corn Letter of March 23, 1937, p. 13) has no distinctly visible effect on su2. Three separate crosses of du x su2 were made and F1s selfed. Six ears from each F2 showed no definite effect of du on su2. Any such effect is very slight if existent at all. Therefore, the mechanisms by which the su1 and su2 genes act must be different, at least in part.