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THE AMERICAN NATURALIST [Vol. XLIV 



inheritance, but there is another interpretation which may 

 apply in certain cases. I have repeatedly tried to cross 

 Giant Missouri Cob Pipe maize (14 feet high) and Tom 

 Thumb pop maize (2 feet high), but have always failed. 

 They both cross readily with varieties intermediate in 

 size, but are sterile between themselves. We may 

 imagine that the gametes of each race, though varying in 

 structure, are all so dissimilar that none of them can unite 

 to form zygotes. Other races may be found where only 

 part of the gametes of varying structure are so unlike that 

 they will not develop after fusion. The zygotes that do 

 develop will be from those more alike in construction. 

 An apparent blend results, and although segregation may 

 take place, no progeny as extreme as either of the parents 

 will ever occur. 



I may say in conclusion that the effect of the truth of 

 this hypothesis would be to add another link to the in- 

 creasing chain of evidence that the word mutation may 

 properly be applied to any inherited variation, however 

 small; and the word fluctuation should be restricted to 

 those variations due to immediate environment which do 

 not affect the germ cells, and which — it has been shown— 

 are not inherited. In addition it gives a rational basis 

 for the origin of neir characters, which lias hitherto been 

 somewhat of a Mendelian stumbling-block ; and also gives 

 the term unit-character less of an irrevocably-fixed-entity 

 conception, which is more in accord with other biological 

 beliefs. 



