A. B. Stout 89 



Eleven cultivated varieties directly derived from the blackberry and 

 propagated vegetatively were found to be self-compatible, while of 

 twelve varieties descended from the dewberry ten are self-incompatible. 

 Wild plants of the blackberry (Ruhus villosus) were found to be self- 

 compatible. Thus it appears that R. villosus is a self-compatible species 

 while R. trivialis is strongly self-incompatible. 



Of the varieties known to be hybrids between these two species, 

 three (McDonald, Sorsby and Spalding) are self-incompatible and one 

 (Rathbun) is partially self-incompatible. 



Further data are needed to determine fully whether the compati- 

 bility or incompatibility of the hybrid varieties is ever complete and 

 absolute, but it is clear that the self-incompatibility characteristic of 

 one parent appears in various degrees in the different individuals of the 

 F^. It is reported that the self-compatible plants when self-pollinated 

 " produce apparently as good fruits as when cross-pollinated." In regard 

 to cross-compatibility it is reported that most crosses give successful 

 fertilization ; evidently no decided cases of cross-incompatibility were 

 found. 



Detjen finds that, in addition to sterility from physiological incom- 

 patibility, certain hybrid varieties of the dewberry-blackberry cross are 

 also more or less sterile from impotence of sex organs, as is common in 

 inter-specific hybrids. 



A most decided case of variation in sex relations has been reported 

 by Sirks (1917) in the study of cross-incompatibilities in the herma- 

 phrodite species Verhascum phoeniceum. Here the reciprocal crossing 

 between pairs of plants gives all grades of opposite results in immediate 

 fertility. In the extremes, both crossings may be highly and perhaps 

 absolutely compatible, or they may be incompatible, or one may be 

 compatible and the other incompatible. In the latter case using one 

 plant as a male and the other as a female gives full compatibility ; 

 reversing the relation gives complete incompatibility. Furthermore 

 there are many grades in the comparative fertility of reciprocal crossings 

 between two plants. 



This evidence agrees with that which the writer (1916) has presented 

 for chicory, but Sirks' data are much more extensive and conclusive. 

 It may be stated here that while Sirks has not reported on the self- 

 compatibilities of V. phoeniceum, my own studies with this species, to be 

 reported later, show that in my strains at least there appears to be no 

 tendency for an end-season change in compatibility that might lead to 



