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. 
