HEREDITY — BATESON. 371 



dividuals, 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 " w as 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, prob- 

 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 

 histor}^ it produced at least two marked varieties, which I can only 

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

 of forms we 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. Kelative 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 unesceptionable cases. 



