i 9 22] STOUT— STERILITY I2Q 



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 Sachs (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 

 (Child i). 



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 



