28o Reversion and [ch. 



indicated, as she points out, that the red anthocyan is 

 probably a glucoside formed by a combination of tannic 

 acid with a sugar. Now in this case Miss Wheldale found 

 that the "ivory" flowers do contain a glucoside and that 

 this body is absent from the white flowers. The breeding 

 experiment proves that the white variety introduces a red- 

 dening factor which is absent from the "ivories." According 

 to her view the contribution which the "ivory" makes is 

 the glucoside, and the complementary contribution made by 

 the white is an oxidase which acts upon the glucoside to 

 make anthocyan. 



With the development of the inquiry it has become clear 

 that variation, in so far as it consists in the omission of 

 elementary factors, is the consequence of a process of 

 '^unpacking." The white Sweet Pea was created in the 

 variation by which one of the colour-factors was dropped out. 

 Such variation is not, as it was formerly supposed that all 

 variation must be, a progress from a lower degree of com- 

 plexity to a higher, but the converse. When from a single 

 wild type, man succeeds in producing a multitude of new 

 varieties, we may speak of the result as a progress in 

 differentiation : but we must recognize that the term is only 

 applicable loosely, and that the obvious appearance of 

 increased complexity may in reality be the outcome of a 

 process of simplification. The facts nevertheless preclude 

 the suggestion that all variation even under domestica- 

 tion is of this nature, nor till experimental research has 

 developed far beyond its present limits, can we make any 

 confident estimate whether it is the one process or the other 

 which has played the larger part in the formation of the 

 diversity of living forms. 



It is legitimate to conclude from what is known of 

 reversionary cases that when reversion in characteristics 

 other than colour results from crossing, similar processes 

 are operating. One such instance was described in con- 

 nection with the peculiar properties of colour-factors (p. 133), 

 a reversion to the hoary leaf resulting from the cross of two 

 glabrous types of Stock {MattJiiold). As yet however the 

 only other example of reversion in a structural character is 

 that furnished by the crosses between two varieties of Sweet 

 Peas known as Bush and Cicpid, The Cupids are the 



