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THE AMERICAN NATURALIST [Vol. XLIII 



nant characters could be present, and these two would present a 

 case of what Bateson calls spurious allelomorphism, for they 

 would separate from each other in the reduction division. 



It is clear, therefore, that the presence in a species of more 

 Mendelian character pairs i presence and absence constituting a 

 pair) than there are chromosomes does not prove that Mendelian 

 characters do not appertain to the chromosome as a whole. If, 

 however, in a species having one pair of chromosomes we could 

 get into a single individual more independent character pairs 

 than two, or if we can get even two dominant characters that are 

 independent of each other, and not allelomorphic to each other, 

 then we should have proven that Mendelian characters do not 

 appertain to whole chromosomes. In general, if, in a species 

 having 2n chromosomes, we can bring together in a single indi- 

 vidual more than n independent dominant characters, no two 

 of which are allelomorphic to each other, then it would be proved 

 that Mendelian phenomena are not simply phenomena of the 

 chromosomes. In a recent communication to the writer. Dr. 

 Baur recognizes the justice of the above point of view and hopes 

 to be able to test the matter in the near future. Dr. Shull will 

 make a similar test at the Cold Spring Harbor Station. This, 

 it would seem, is a simple and direct method of testing the 

 validity of the theory advaneed by many investigators, that the 

 chromosome itself is the basis of the so-called unit character. 



Even if this theory should be substantiated, it does not follow 

 that the chromosome represents a unit character in the sense in 

 which the term unit character is understood by most Mendelists. 

 Shull has very justly pointed out 1 that "there is no evidence of 

 the existence of a pair of internal unite (allelomorphs)." The 

 term "unit" has been applied to Mendelian characters on the 

 assumption, which I regard as untenable, that there is in the 

 germ plasm a definite organ set aside for each hereditary char- 

 acter. An elaborate theory of inheritance and evolution (De 

 Vries) has been erected on this assumption. Mendelian phe- 

 nomena can be explained in a wholly different manner, and one 

 which is more consistent with the idea of the chemical basis of 

 life processes, as the following illustration shows. 



Let us designate the chromosome pairs in our common domesti- 

 cated cattle as A, B, C, . . . L. Let us assume that the chromo- 

 somes in each of these pairs are capable of several types of 



