Nov., 1923] STOUT — PHYSIOLOGY OF INCOMPATIBILITIES 461 



self-compatibility is preceded and followed by self-incompatibility. There is 

 alternative expression of extreme grades of compatibility and incom- 

 patibility in the series of flowers produced in succession on the same branch. 

 The functions of fertilization are in such cases operating in a cycle of 

 intensities. 



It may here be reported that, in the species Brassica pekinensis, self- 

 incompatibility of a plant as a whole or of a family of plants may be de- 

 cidedly changed by a cultural treatment which reduces vegetative vigor. 

 In a family of this species grown for three generations, less than 10 percent of 

 the total of 326 plants were highly self-compatible and there was no hered- 

 itary effect of selection for self-compatibility. When a generation of this 

 family was grown in small pots with decided reduction of vegetative vigor, 

 of a total of 1,128 plants there were 734 (65%) that were highly self-com- 

 patible, and only 22 (less than 2%) were self -incompatible. Furthermore, 

 a large proportion of the former were self-compatible in the earliest flowers 

 that opened. The family was decidedly changed in regard to the number 

 of plants that were self -compatible, and in the individuals the characteristic 

 cycle was altered. Such results, together with the other behavior noted 

 above, indicate that there is a direct and very decided physiological correla- 

 tion between vegetative vigor and the functional properties of the organs 

 concerned with fertilization. 



This is at least suggestive that the physiological conditions which 

 restrict and limit indiscriminate fertilization within species are not only 

 subject to internal regulation, but that in some cases at least they are corre- 

 lated with changes in vegetative vigor. 



The situation gives hope that the cyclic expression of sexual affinities 

 and the development of extremes of compatibility may be so regulated 

 experimentally that the specific biogenetic factors and conditions operating 

 in this highly specialized differentiation may be determined. 

 New York Botanical Garden 



