I922 ] STOUT— STERILITY in 



parts in seed formation, may be obtained by experimental means 

 from a study of the fluctuations in fertility that are to be seen in 

 those feebly self-compatible individuals which are to be found in 

 species in which general sexual incompatibilities are strongly 

 developed. 



A subsequent report of a more detailed study on this problem 

 (Stout ii), however, showed that in Verbascum phoeniceum, 

 Eschscholtzia calif omica, and Cichorium Intybus the various grades 

 of self-compatibility operate very uniformly throughout the entire 

 period of bloom, and that there are in the feebly self-compatible 

 plants of these species no specially marked tendencies to self- 

 compatibility at any definite phase of the blooming period. It was 

 also found that in Nicotiana Forgetiana Hyb. Hort. and in Lytkrum 

 Salicaria end-bloom self-compatibility develops as an infrequent 

 individual variation rather than as a phenomenon characteristic of 

 the self-compatible plants. In these species there is no cyclic pro- 

 duction of fruits and seeds which would indicate a general relation 

 between vegetative vigor and the development of self-compatibility. 



Such a cyclic occurrence of self-compatibility was found, 

 however, and reported for Brassica pekinensis, and it was noted 

 that the highest degree of self-compatibility attained by any given 

 plant appeared very uniformly during the period of mid-bloom. 

 Further studies with this species have since been made which show 

 this to be the rule for all those individuals that are self-compatible 

 in any degree. Similar behavior has also been found in cultures of 

 Brassica chinensis and in hybrids between this species and B. 

 pekinensis. So far as known to the writer, this is the most uniform 

 and definite case of a general and definite periodicity in the modifi- 

 cation of sexual compatibilities within a blooming period. In 

 these species, also, flower abortion appears in the transition of 

 vegetative to reproductive vigor, exhibiting an influence of vege- 

 tative vigor on the morphological development of flowers. 



Material and methods 



Several strains of the "head" sorts of Brassica pekinensis, 

 commonly known as Chinese cabbage or Pe-tsai, and one strain of 

 the loose-leaved or headless sort (the Nanking variety) were grown 



