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THE AMERICAN NATURALIST 



[Vol. LII 



ferent germplasms, restored by means of protandry, 

 protogyny or self-sterility. 



In even such a brief consideration of the more im- 

 portant changes which have occurred in the reproductive 

 mechanisms of animals and plants, one thing stands out 

 impressively. Both animals and plants have adopted as 

 the most acceptable and satisfactory modes of reproduc- 

 tion, methods which are identical in what we deem to be 

 the essential features, something that can be said of no 

 other life process. These significant features are the 

 preparation of cells which in general contain but half of 

 the nuclear material possessed by the cells from which 

 they arise, which are differentiated into two general 

 classes that show attraction toward each other, and which 

 will fuse together in pairs to form the starting point of a 

 new organism. This parallel evolution is of itself valid 

 evidence of the importance of the process. Let us return 

 to our original proposition for its interpretation. 



First, is there any evidence that sexual reproduction 

 differs from asexual reproduction in what may be called 

 the heredity coefficient? In other words, does one method 

 hold any advantage over the other as an actual means for 

 the transmission of characters? I have answered this 

 question in the negative, but it must be confessed that the 

 basis for this answer is a long and intimate experience in 

 handling pedigree cultures of plants rather than the study 

 of a large amount of quantitative data bearing directly 

 on the problem. Quantitative data are to be found, of 

 course, and plants furnish the best material because of the 

 ease m handling large numbers of both clons and seedlings 

 side by side; but even with the best of plant material, 

 several undesired variables are present. Practically the 

 inquiry must take the form of a comparison between the 

 variability of a homozygous race when propagated by 

 seeds and when propagated by some asexual method. 

 The first difficulty is that of obtaining a homozygous race 

 and thus eliminating Mendelian recombination. The 

 traditionally greater variability of seed-propagated 



