stout: pollinations in cichorium intybus 423 



and the various fruit-bearing plants generally described as self- 

 sterile. In chicory the sporadic occurrence of plants self-fertile in 

 varying degrees has given opportunity to observe the comparative 

 vigor of self-fertilized and cross-fertilized progenies. There has been 

 no consistent apparent decrease either of vegetative vigor or in 

 the production of flowers in these self-fertilized lines. Different 

 lines of descent differ widely in respect to habit of growth, size, 

 and total number of flowers produced per plant. Some families 

 of the F3 generation were uniformly small, scraggly, sparsely 

 branched plants, others were short but very bushy and much 

 branched, and still others were tall, vigorous, and much branched. 

 These differences seem to be independent of any differences in 

 the degree of homozygosity and in each family self-fertile and self- 

 sterile plants were most often as nearly identical in habit of growth, 

 vigor, and in number of flowers produced as it is possible for two 

 plants to be. The evidence on this point is still accumulating and 

 more complete statistical data will be published later. 



The co7itrast between sterility from physiological incompatibility 

 and sterility from impotence. — Sterility due to physiological in- 

 compatibility is quite different from that due to impotence as I 

 have limited these terms above. The distinction has not generally 

 been made and from the discussions given in the literature one 

 can not always determine what sort of sterility actually prevailed. 

 In such discussions of infertile hybrids as that by Wilson ('06) 

 and by East and Hayes ('12), the different sorts are treated 

 without any distinction. The sterility which East ('15a) reports 

 for hybrids between Nicotiana Forgetiana and N. alata grandiflora 

 is evidently due solely to a physiological incompatibility (germ 

 cells all fertile in other connections), while that which he reports 

 ('156) for hybrids of N. rustica X N. paniculata is evidently purely 

 a matter of impotence (failure to produce spores or gametes). 

 In 1912 East & Hayes reported the former hybrid as "fertile" 

 and the latter "partially fertile." That a limitation in the 

 use of terms is necessary is clearly apparent in such cases. 



The causes of impotence which result in degeneration of spores, 

 especially as seen in many interspecific hybrids, it would seem, are 

 more essentially intracellular in that the incompatibility may 

 involve a direct relationship within the cells between their idio- 

 plasmic elements, giving the so-called "chromatin repulsion." 



