SELECTIVE FERTILIZATION IN POLLEN MIXTURES. 255 



plants manifest a decided preference for their own kind of pollen. 

 This is a result which would have surprised students of flower 

 pollination in Darwin's time but which, as I shall attempt to 

 point out later, is in agreement with other results from biological 

 investigation. 



METHODS OF CARRYING ON THE EXPERIMENTS. 



In an investigation in which it was desired to compare the 

 chemical composition of seeds of maize having different genetic 

 constitution but produced under as nearly identical conditions 

 as possible advantage was taken of endosperm characters to 

 enable proper classification of seeds produced in the same inflores- 

 cences. For example, two kinds of pollen carrying yellow endo- 

 sperm color and white endosperm color were mixed together 

 and applied to a plant which normally produces uncolored seeds. 

 The resulting yellow and white seeds were distributed at random 

 on the pistillate spikes and were as nearly comparable in respect 

 to external and nutritional factors as it is possible to obtain. 

 It was found that such pollen mixtures could be applied to both 

 strains furnishing the pollen and the two kinds of seeds easily 

 distinguished. On the white-seeded strain the seeds resulting 

 from the plant's own pollen were white and the cross-fertilized 

 seeds yellow. On the yellow-seeded plants the self-pollinated 

 endosperms were dark yellow while the crossed seeds were dis- 

 tinctly lighter in color, in most cases they had a white cap, and 

 were as a rule readily separable. 



Attention is directed to the fact that the material used for 

 these mixed pollinations consisted largely of inbred strains which 

 had been reduced to uniformity and constancy so that the 

 genetical differences between the two kinds of seeds sharply 

 differentiated them, much more than in ordinary cross-pollinated 

 varieties of this plant in which the yellow color is usually variable 

 due to more than one factor for this color and various modifying 

 conditions such as the consistency of the endosperm in respect to 

 corneous and floury starch. 



A number of pairs of plants were treated in this way by mixing 

 their pollen and applying to both types. After harvesting it was 

 realized that here was an excellent method of determining 



