152 



BROOKLYN BOTANIC GARDEN MEMOIRS 



TABLE 11— Continued 



reciprocal, Cross No. 2. In the classes A, B and C the proportions 

 were 18, 10, 10 and 4, 6, 2 respectively. This similar behavior of the 

 progeny of reciprocals seems to us strong corroboratory evidence in 

 favor of the conclusion that reciprocal crosses always behave in like 

 manner as regards self-sterility. 



The study on this family is but one of several that have been 

 made but we believe that the data on it alone show unmistakably that 

 the behavior of self-sterile plants in intercrosses is governed by a 

 /relatively small number of factors which act through pollen as if the 

 pollen grain possessed the characters of the sporophyte from which it 

 came, and that the gametes of plants having like constitutions as re- 

 gards effective* factors are incompatible in the sense that they do not 

 make a normal pollen-tube growth and hence do not reach the ovary 

 in time for fusion to occur. This interpretation shows both why 

 plants are self-sterile and cross-sterile. It accords completely with 

 the fact that a population of plants may be divided into groups on the 

 basis of their mating proclivities and that each member of any group is 

 cross-sterile with every other individual of that group although it is 

 fertile with every individual of every other group. 



These assumptions being true, it ought to be possible by con- 

 tinuous self-fertilization, utilizing end-season pseudo-fertility, to 

 obtain ultimately a population in which every individual possesses 

 the same effective self-sterility factors. In such a population all of 

 the plants will not only be self-sterile, but will be cross-sterile. Such a 

 population has been obtained. 



