96 FertillUi in Cichorium intybiis 



individual. The similarity is thus considered as independent of the 

 degrees of dissimilarity in the germ plasm brought about by the 

 crossing necessary to give fertility. 



Beginning about 1910, the attention of various investigators was 

 especially directed to a study of the breeding performance of plants 

 with respect to self-sterility in the attempts to determine its heredity 

 and obtain clues as to the nature of the processes involved. 



In 1911, Baur claimed that the self-sterility of AntiiThivum molle 

 was recessive to self-fertility in A. majus, giving complete self-fertility 

 in all plants of the F^. The F.,, it was reported, was composed of a 

 large proportion of self-fertile plants. Compton (1912, 1913) likewise 

 supports the view that self-fertility is a simple dominant over self- 

 sterility, and further interprets breeding results in Reseda on the basis 

 of a simple presence and absence hypothesis, the absence of some sub- 

 stance, either nutritive or stimulating to the growth of pollen-tubes 

 giving self-sterility, while the presence of such a substance gives self- 

 fertility. Neither Baur nor Compton presents adequate data for his 

 conclusions, and evidently both assumed a Mendelian behaviour of self- 

 sterility and self-fertility on a priori grounds. In regard to the latier 

 generations of these Antirrhinum hybrids, Lotsy (1913) reports that the 

 Fo generations are composed of self-fertile and self-sterile plants, and 

 that there are various degrees of self-fertility in evidence. The state- 

 ment is made by both Baur and Lotsy, however, that all plants of the 

 species A. molle are self-sterile. 



Such interpretations have an advantage of appearing definite, simple, 

 and conclusive. However, the performance in chicory of pedigi'eed 

 cultures of offspring of self-sterile plants does not show any such simple 

 and regular behaviour. Similar methods of study may reveal quite 

 identical conditions and results in the above named species. 



Correns, in 1912, announced the very important discovery of ph3'sio- 

 logical cross-incompatibility among sister plants grown in the F^ seed 

 progeny of a cross between two self-sterile plants of Cardainine 

 pratensis, a species which had previously been known as self-sterile. 

 Correns thus proved, for the first time, that cross-sterility may exist 

 within a variety among plants of seed origin which exhibit no dimorphism 

 or trimorphism. By a groujDing of the results, Correns arrived at a 

 Mendelian analysis of the hereditary performance. Line stuffs were 

 assumed to be represented and transmitted in the germ cells by anlagen, 

 and it was assumed that there could be no fertilization between gametes 

 carrying the same line stuff. An examination of Correns' actual results 



