5. There is a highly significant increase in crossing over in the A₂-Bt and Bm₁-Pr regions of chromosome 5 in microsporocytes as compared with megasporocytes. In a "low" line there was 7.6% recombination between A₂-Bt in the female gametes contrasted with 12.2% in the male gametes. Similar differences between the frequency of crossing over in the two sexes is the explanation of the inexplicable difference found by the writer (1936) in crossing over for the Bm₁-Pr region in plants hyperploid for the short arm of chromosome 5 as compared with diploid sibs. The hyperploid individuals had been used as the male parent while the diploid sibs had been used as the female.

M. M. Rhoades