HEEEDITY — BATESON. 371 



dividiials, gives off, as it did a few years since, a salmon-colored 

 variety, " Coral King," we might claim this as a genuine example of 

 variation by loss. The new variety is a simple recessive. It differs 

 from " Crimson King " only in one respect, the loss of a single color- 

 factor, and, of course, bred true from its origin. To account for the 

 appearance of such a new form by any process of crossing is exceed- 

 ingly difficult. From the nature of the case there can have been no 

 cross since "Crimson King" was established, and hence the salmon 

 must have been concealed as a recessive from the first origin of that 

 variety, even when it was represented by very few individuals, j)rob- 

 ably only by a single one. Surely, if any of these had been hetero- 

 zygous for salmon this recessive could hardly have failed to appear 

 during the process of self-fertilization by which the stock would 

 be multiplied, even though that selfing may not have been strictly 

 carried out. Examples like this seem to me practically conclusive.^ 

 They can be challenged, but not, I think, successfully. Then again 

 in regard to those variations in number and division of parts which 

 we call meristic, the reference of these to original cross-breeding is 

 surely barred by the circumstances in which they often occur. There 

 remain also the rare examples mentioned already in which a single 

 wild origin may with much confidence be assumed. In spite of re- 

 peated trials, no one has yet succeeded in crossing the sweet pea with 

 any other leguminous species. We know that early in its cultivated 

 history it produced at least two marked varieties, which I can only 

 conceive of as spontaneously arising, though, no doubt, the profusion 

 of forms w^e now have was made by the crossing of those original 

 varieties. I mention the sweet pea thus prominently for another 

 reason, that it introduces us to another though subsidiary form of 

 variation, which may be described as a fractionation of factors. 

 Some of my Mendelian colleagues have spoken of genetic factors as 

 permanent and indestructible. Relative permanence in a sense they 

 have, for they commonly come out unchanged after segregation. But 

 I am satisfied that they may occasionally undergo a quantitative dis- 

 integration, with the consequence that varieties are produced inter- 

 mediate between the integral varieties from which they were derived. 

 These disintegrated conditions I have spoken of as subtraction — or 

 reduction — stages. For example, the Picotee Sweet Pea, with its 

 purple edges, can surely be nothing but a condition produced by the 

 factor which ordinarily makes the fully purple flower, quantitatively 

 diminished. The pied animal, such as the Dutch rabbit, must simi- 

 larly be regarded as the result of partial defect of the chromogen 

 from which the pigment is formed, or conceivably of the factor which 



1 The numerous and most interesting " mutations " recorded by Prof. T. H. Morgan 

 and his colleagues in the fly, Drosophila, may also be cited as unexceptionable cases. 



