



CYCLIC MANIFESTATION OF STERILITY IN BRASSICA 

 PEKINENSIS AND B. CHINENSIS 



A. B. Stout 

 (with SEVEN figures) 



The transition from asexual or vegetative growth to the con- 

 dition of flower and fruit production in hermaphrodite plants is 

 to be recognized as a most fundamental aspect of sexuality. 

 Furthermore, the inter-relations that exist between vegetative and 

 reproductive vigor and the influence of the former on the latter 

 are reflected and exhibited in certain phenomena of sterility. 



It is now certain that vegetative vigor and the internal inter- 

 relations incident to it may limit reproductive vigor and sexuality. 

 The limitation from these causes may take place in two ways: (i) 

 they may interfere with or influence the morphological development 

 of flowers or other reproductive organs, and (2) they may affect the 

 functioning powers of organs that are fully formed. If these influ- 

 ences are marked, one or more types of sterility may appear. 



Only recently observations have indicated that, at least in 

 some cases, the compatibilities and the fertility of the sex organs 

 may vary rather definitely within the cycle of vegetative and 

 reproductive development characteristic of the particular species. 

 A phenomenon of this sort is reported by East and Park (4), 

 who found that in the few plants which are self-compatible in 

 certain species and hybrids of Nicotiana, the self-compatibility 

 develops only at the end of the flowering period. Cases of cross- 

 compatibility appearing only at the end of the period of bloom are 

 reported also. A very decided case of the development of self- 

 compatibility only at the close of the period of bloom was observed 

 by the writer, in a plant of Lythrum Salicaria, and reported at the 

 annual meeting of the Botanical Society of America for 191 7. 

 These observations suggested that new evidence on the old problem 

 of the relation between vegetative vigor and reproductive vigor, 

 as expressed in the formation of flowers and the functioning of the 



Botanical Gazette, vol. 73] [no 



