1922] STOUT—STERILITY 129 
It is not to be considered, however, that a single simple change 
in nutrition is the sole biogenetic factor regulating the appearance 
of maturity and its attending morphogenesis of flowers. In flower- 
ing plants, such as the species of Brassica whose sterilities are 
reported in this paper, there is progressive differentiation of parts 
in reference to metabolic activities which is most obvious in respect 
to the manufacture, distribution, and consumption of food. It has 
been shown that there are also special stimulating and inhibiting 
influences which in a decided manner regulate and correlate 
development. That these influences may be substantive and 
special (but metabolic) and different from food materials was 
postulated by Sacus (8) in one of the latest of his papers; that some 
influences are stimulative and correlative in the sense of nervelike 
impulses or even electrical stimuli have repeatedly been shown in 
studies of the nature of transmission and excitation in phenomena 
of dominance and control in correlative growth and development 
(Cuitp 1). 
It is to be noted that the complete life cycle of flowering plants 
involves two periods of vegetative vigor and maturity; one for the 
sporophyte and one for the gametophyte. The former culminates 
in the production of spores and the latter in the production of 
gametes. The generations are antithetic. In its length of life, 
vigor of vegetative growth, and reproductive power (number of 
gametes), the gametophytic phase has become relatively weak and 
highly specialized. In the sporophyte great vegetative vigor is 
correlated with great reproductive vigor in the production of spores 
(which are, however, in themselves asexual) and in the nurture of 
the gametophyte and the embryo. Sex differentiation in the great 
group of flowering plants has been pushed back during the progress 
of evolution into the sporophytic stage of the entire cycle, and here 
sexuality now culminates in seed formation in which the nutrition 
of the embryo is a most important factor. Sexual reproduction in 
these higher plants has become more and more inter-related with 
the vegetative phase of the sporophyte and subject to its internal 
and biogenetic regulation. 
The decided influence of such regulation is seen in the fact that 
in the great group of hermaphrodite plants, the whole trend of the 
