1922] STOUT—STERILITY 127 
alternation of vegetative and reproductive vigor. Flower abortion 
occurs normally as a transitional stage between the formation of 
green leaves and the production of functional sporophylls. Those 
plants which exhibit flower abortion are not able to pass directly 
from producing green leaves or leaves with branches at the nodes to 
the production of flowers, and flower abortion occurs as a transitional 
stage. The abortion of flowers appears in the phase where vege- 
tative vigor is waning, but before reproductive vigor is fully in 
evidence. There is also a marked agreement among the various 
branches of a plant as to the grade of development reached at any 
one date of blooming (figs. 1-3), which indicates a definite relation 
between the condition causing flower abortion (and also normal 
flower formation) and a condition of the plant as a whole. These 
phenomena, therefore, have many aspects characteristic of physio- 
logical correlation. 
The arrested development of flowers at the ends of branches 
after a period of vigorous blooming of the plant is obviously due 
to an extreme waning of vigor and the approaching death of the plant 
as a whole, and of course is a phenomenon prevalent in all sorts of 
plants. Axial proliferation from the pistils is to be considered as a 
resumption of vegetative growth after the differentiation of the 
pistils has been accomplished. 
Turning to the functional relations of the sex organs in these 
two species of Brassica, at least to the compatibility in self- 
fertilization, it is seen that they also exhibit a periodicity on their 
occurrence which forms a very definite cycle. A total of 718 plants 
that were self-compatible to some degree have now been observed 
in these two species and in hybrids between them. With the excep- 
tion of a few individuals in which pods developed irregularly, the 
maximum of self-compatibility was reached during the mid-bloom 
of the plant (figs. 2, 3, 5-7). Previous to and following this period, 
the self-compatibility grades into complete self-incompatibility or 
into a much weaker grade of self-compatibility. Furthermore, the 
climax of self-compatibility is remarkably coordinated among the 
different branches according to the time of blooming quite as is 
the earlier development of flower abortion. 
The remarkably uniform development of self-compatibility 
during the time of mid-bloom in Brassica chinensis, B. pekinensis, 
