388 A. B. STOUT 



cherry, blueberry, etc., it is somewhat surprising that more searching 

 studies have not been made on the sporadic occurrence of self-fertile 

 plants. It is somewhat in doubt, therefore, whether there exists a 

 species, a variety, or even a strain of plants in which self-sterility due 

 to physiological incompatibility is absolute. However, such may exist 

 especially among certain hybrid strains as is suggested by East's 

 data. Many further data are needed to allow of any adequate state- 

 ment of the various degrees and intensities of such self-sterility in 

 species or in different strains as a whole. The general evidence, how- 

 ever, suggests that in many such cases the sporadic occurrence of 

 self-fertile plants may be quite as it is in chicory. 



The almost complete self-incompatibility of the Fi progeny of the 

 crosses between plants of the "red-leaved Treviso" variety and the 

 wild white-flowered plant A is noticeable. The occurrence of only 

 two self-fertile plants of feeble fertility out of 73 such plants emphasizes 

 the sporadic nature of the development of self-compatibility. This 

 may also be considered as evidence that wide crossing inside the 

 species does not especially favor the development of self-compati- 

 bility. In fact, a comparison of the behavior of these plants with 

 that of the 1916 crop of the inbred plants of the "red-leaved Treviso" 

 variety leads to the conclusion that inbreeding is more favorable to 

 the development of self-compatibility than is wide crossing. In East's 

 .results (1915) all plants tested, some 500 in number, of the Fi, F2, F3, 

 and F4 generations were found to be self-sterile. As these were the 

 offspring of an interspecific cross, it does not seem that wide crossing 

 has here favored the development of self-compatibility. It should be 

 noted that East suggests that there may be some increase in the 

 development of cross-incompatibilities among the later generations, 

 which he considers may be due to an increased homozygosity, but 

 the evidence is not conclusive on this point. 



I have not sufihcient data to judge adequately of the frequency of 

 cross-incompatibilities among the various series and generations of 

 chicory grown. Cross-incompatibility has occurred in each generation 

 of the red -leaved Treviso variety (for data obtained in 1914 and 191 5 

 see Stout, 1916, Table 14) as it has in all other families thus far tested 

 (Stout, 1 9 16, Tables 9-13). Everywhere that I have tested for cross- 

 incompatibility in chicory it has been found to be very general and to 

 exist in various grades of intensity. 



The numbers of self-fertile plants which appeared among the Fi 



