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THE AMERICAN NATURALIST [Vol.XLVI 



not to be determined from the data presented whether 

 the correlated characters were derived from the same or 

 different parents. This phenomenon of coherence, which 

 appears to most field naturalists and practical breeders 

 as a well-known fact, strikes the followers of Mendel as a 

 novel idea, to judge from the following (Bateson & Pun- 

 nett, 1911, p. 6) : 



the original parents can influence the distribution of the factors 

 among gametes of F 1 introduces a new conception into ueiH'tir phys- 

 iology. 



The difficulty of " breaking up" combinations of char- 

 acters has so long been a stumbling block to breeders that 

 to them the conception can hardly be considered new. 

 The suggestion that the number of individuals in which 

 two characters are combined bears a definite relation to 

 the number in which they occur singly is without doubt a 

 direct outgrowth of Mendelian investigations and meth- 

 ods of thought. Perhaps this latest application of 

 mechanical conceptions to biology may stimulate research 

 as did Mendel's original discovery. On the other hand, 

 there are many who think that the application of Mende- 

 lian formulas has already been pursued to an absurd 

 point by the factoring and subf actoring of characters and 

 the assumption of intensifying and inhibiting determi- 

 nants. Those not already abreast of Mendelian literature 

 are not likely to be impressed with the further refinement 

 that aims to devise formula? for expressing gametic 

 relations between two of these already complicated Men- 

 delian systems. 



In considering the relation between two Mendelian 

 characters four possible combinations are involved. 

 Thus, if A and B be taken to represent the appearance of 

 the two characters, and a and b their non-appearance, 

 these four combinations would be expressed as follows: 

 AB, Ah, a B, and ab. The theory of gametic coupling 

 assumes that an attraction or other unknown relation 

 exists between the determinants of the two characters, 



