128 BOTANICAL GAZETTE [February 



and hybrids between them, is convincing evidence that the functions 

 of fertilization are here operating in a cycle of intensities. The 

 period of mid-bloom may be considered as the time when conditions 

 are most favorable for fertilization. The cross-fertilizations which 

 are highly effective both previous to and following the maximum 

 for self-compatibility are hence to be considered as indicating a 

 different and possibly a stronger grade of sexual relation. It 

 seems conclusive that, judged by the functional relations in fertili- 

 zation, the physiological properties of the sex organs in these 

 plants vary in a rather definite cycle. 



It is clear that self-compatibility as contrasted with certain 

 grades of cross-compatibility in these species of Brassica is limited 

 to a specific period following the transition from vegetative to 

 reproductive activity and limited by the waning senility of the plant 

 as a whole. Self-compatibility appears coincidently with the 

 climax of the reproductive activity. 



Sexual reproduction itself is generally characterized as a 

 phenomenon of maturity (Coulter 3). The differentiations of 

 sex as indicated by anatomical features and by the physiological 

 compatibilities are perhaps to be considered as a smaller cycle 

 operating within the larger alternation of vegetative and repro- 

 ductive phases and subject to the same biogenetic regulation. 



In the flowering plants especially, there is great diversity 

 among species in the relative development of their vegetative and 

 reproductive habits and in the inter-relations between these two 

 phases. Perhaps the most universal of the biogenetic conditions 

 incident to the transition from the vegetative to the reproductive 

 phase is that change in nutrition which leads to the accumulation 

 of carbon compounds. This is an internal condition that arises in 

 the plant as a whole in the course of maturity, in contrast with 

 relative excess of nitrogenous material that is characteristic of the 

 vegetative stage. The decided influence of nutritive relations in 

 regulating development and in influencing fruitfulness has recently 

 been discussed by Kraus and Kraybill (7), who have emphasized 

 the fact that a well-balanced development, especially in regard to 

 fruitfulness of fruit-bearing plants, is associated with a proper 

 balance between nitrogen and carbohydrate metabolism. 



