Brassica campestris LINN. In one variety a few pollen grains were found on stigmas after self-pollination. The germination of incompatible pollen was poor. Pollen-tube length usually was about as long as the diameter of a pollen grain. Practically all pollen-tubes did not penetrate into the stigma. However, only a few emptied grains and tubes of considerable length were also found. Some tube ends were spirally coiled around the papillae. The results of cross-pollinations were decidedly superior in the total number of pollen grains on the stigma, in the percentage of pollen germination, and in the number of emptied grains to those of the self-pollinations. The tissue of the stigma was penetrated freely by the pollen-tubes. The longest tubes reached the ovary in about 5 hours after pollination. In the other variety numerous pollen grains were found on the stigma after self-pollination. The percentage of germination of incompatible pollen was higher than that of the former. In other respects, however, the behavior found for pollen and pollen-tubes after self-pollination was an approximately equal to that of the former. Brassica napus LINN. As already known Brassica napus is a self-compatible plant. There were no differences between self-pollinations and cross-pollinations in the percentage of pollen germinationon the stigma, in the number of emptied grains, and in the rate of pollen-tube growth. Brassica Rapa LINN. The results of self-pollinations showed decreased germination of incompatible pollen and no penetration of tubes into the stigma. Only a few emptied grains and tubes into which penetrated the ovary were also found. Some tube ends were spirally coiled around the papillae. The behavior of pollen and pollen-tubes after cross-pollination was proved to be analogousto that of Brassica campestris. The pollen-tubes penetrated freely into the tissue of the stigma. The longest tubes reached the ovary in about 8 hours after pollination. In conclusion, it may be stated that Brassica napus is a self-compatible plant, and that in Brassica campestris and B. Rapa self-incompatibility is due generally to decreased germinationof incompatible pollen and to no penetration of tubes into the stigma, although certain variety of Brassica campestris shows a high percentage of germination of incompatiblepollen.