SELECTIVE FERTILIZATION IN POLLEN MIXTURES. 253 



and to accomplish fertilization. East considers that chance 

 segregation in the germ cells and random mating of these germ 

 cells is a fundamental genetic hypothesis applicable to plants 

 and animals alike. With this conclusion the writer is in accord, 

 with the reservation that the evidence from gametic abortion 

 should not be put aside as belonging to a different category. 



The data to be presented here bear upon another phase of the 

 problem. The above conclusion, it should be clearly kept in 

 mind, applies only to gametes produced by one or more indi- 

 viduals of the same type. That is, the gametes may be unlike 

 in the factors they carry, but if they come from the same or 

 similar individuals they are potentially equal in ability to 

 fertilize. But what is the result when germ cells from two 

 individuals of different type are presented at the same time in 

 excess so that not all can fulfill their function? Will fertilization 

 take place at random or not? This is the problem to be con- 

 sidered here. In the one case doses of different kinds of medicine 

 come in the same capsules. In the other the capsules as well 

 as their contents may differ. Anyone accustomed to swallowing 

 a particular kind of capsule made of a familiar substance and all 

 of the same size and shape can take any kind of medicine with 

 equal readiness irrespective of the result which will ensue when 

 the materials within the containers begin to operate. Applying 

 this crude metaphor to plants and animals, in the one case, the 

 germ cells, however they differ in factorial composition, come 

 in the same cytoplasmic envelope; in the other, the cytoplasm 

 as well as the genes may differ. 



It has already been shown that, in particular cases, there is a 

 selective action when pollen from different plants is applied to a 

 stigma at the same time. East (1919) has demonstrated that 

 in a mixture of compatible and -incompatible pollen placed on 

 the stigmas of self-sterile Nicotianas the compatible pollen alone 

 functions. Two experiments were devised to test this. Small 

 numbers of pollen grains were counted out under a microscope 

 and placed on stigmas known to be receptive to that kind of 

 pollen. The stigmas were then covered with a large amount of 

 incompatible pollen. The former only was able to fertilize as 

 shown by the results from eight such mixed pollinations which 



