386 A. B. STOUT 



from four different seed parents of the red-leaved Treviso (Ser. 1-4, 

 Table 2) and 19 were derived from the wild white-flowered plant as a 

 seed parent. All these plants were unmistakably hybrids. In no 

 case did a plant's own pollen function in fertilization. 



It may be noted here that East (1915) has made the suggestion 

 that the physiological conditions operating in self-incompatibility 

 involve a failure on the part of the plant's own pollen to stimulate the 

 proper secretions in its pistil necessary for growth of the pollen tubes. 

 If- this were the case, it would seem that self-sterility might be removed, 

 in part at least, by mixing pollen as I have done in the crosses referred 

 to above. Such, however, was not the result. It is possible that such 

 results might more readily be obtained in species in which the fertiliza- 

 tion processes are much less rapid than in chicory. 



Of the 73 plants of this Fi generation, only tAvo plants were self- 

 fertile with percentages of 5 and 19. In only two cases were the 

 number of heads pollinated less than 10. The results are therefore 

 ver}^ decided. All of these plants were blue-flowered and were quite 

 similar in general vegetative habit and appearance. All flowered pro- 

 fusely throughout the season, and, as is the case with plants having 

 only this type of sterility (physiological incompatibility), all set abun- 

 dant seed in many heads open-pollinated. 



Cross-Incompatibilities among the Plants Grown in 1916 



A brief summary may here be given regarding the results of cross- 

 pollinations made during 19 16. Of the cultures of red-leaved Treviso 

 (R), 37 different plants were tested in a total of 34 different combina- 

 tions; of these 16 were sterile and 18 fertile in some degree. Among 

 the plants of the Fi generation (RA), 24 combinations of cross-pol- 

 linations were made involving 37 different plants. Of these 9 were 

 sterile and 15 were fertile in some degree. As indicated by the figures, 

 the combinations among the R plants involved fewer plants propor- 

 tionally and more reciprocals than did those among the RA plants.' 

 No particular emphasis can be given to the number here obtained in 

 its bearing on the influence of inbreeding or cross-breeding. The 

 data obtained from these plants selected at random, however, indicate 

 that cross-incompatibilities exist in marked degree. The results in 

 this respect are quite in agreement with those already reported (1916, 

 Tables 9-14), not only for the red-leaved Treviso but for other cultures 

 of chicory. 



