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But a thorough search of the available literature fails to reveal any reports on sterility in Cosmos bipinnatus. I n fact, there seems to have been almost no study made on the sterility in any compositae. In the only Cosmos investigations recorded, MIYAKE, IMAI, and TABUCHI (1926,1927) studied inheritance of flower color, pollen color, and floral characters but made no mention of sterility. MATERIAL AND METHODS SUMMARYI . Cosmos bipinnatus is entirely self-sterile. 2. Some plants are inter-fertile while others are inter-sterile.3 . The existence of four allelomorphs for cross-sterility has been established; and the back-cross data indicate the presence of at least an additional fifth factor.4. Any plant gives stimulus only to pollen carrying genes other than its own, and plants of the same genotype are cross-incompatible.