SELECTIVE FERTILIZATION IN POLLEN MIXTURES. 287 



produced from the corners of the phylogenetical triangle. The 

 evolutionary significance of this phenomenon has been ably 

 reviewed by Peal in the above citation so that it is not useful to 

 go into that phase of the problem in detail here. It is interesting 

 to note that the results from maize fulfill his expectation as in 

 conclusion he says, "the fact that we find such a high degree of 

 homogamy in a protozoan form like Paramecium strongly sug- 

 gests the possibility that in higher organisms there may be 

 assortative mating of the gametes in the process of fertilization. 

 Should such a homogamy occur it would probably be of far 

 greater importance than any assorted mating of the somas." 

 While the selective agency in plants does not differentiate be- 

 tween gametes produced by one type in the end the result is the 

 same. Individuals with like characters tend to be brought to- 

 gether and virtually to be set apart from the general population. 



Biological investigations unite to show that the importance of 

 sex is to make organisms more plastic in adaptability. The 

 advantages have been so great that sexual reproduction is now 

 established as the dominant method for the renewal of organism 

 in both kingdoms at the expense of economy and speed of multi- 

 plication. It is not strange then that accessory devices have 

 been developed to insure the fulfillment of the function for which 

 so much has been expended. Self-sterility or self-impotency is 

 one of the means developed to -serve this purpose. 



The reverse phenomenon, that of self-prepotency, so far is 

 shown among plants only by maize. It would be surprising to 

 find it limited to this one species. Is it not more likely to be a 

 general manifestation? As a fundamental principle it may apply 

 even to those organisms which show self-sterility, this latter 

 being a special adaptation entirely overcoming the handicap 

 placed upon unfamiliar gametes in order to make certain the 

 advantages which exogamy holds out. One cannot insist upon 

 such an assumption with evidence from only one or possibly 

 two species. But the evidence, limited though it may be for 

 the present, is one more indication that homogeneity, similarity, 

 likeness, familiarity, or however it may be described, in proto- 

 plasmic structure is consistent with and favorable to the highest 

 physiological efficiency. 



