Note then
(1) That Nobbe does not specify which colours he crossed together, beyond the fact that white was crossed with each fertile form. The crimson form (Karmoisinfarbe), being double to the point of sterility, was not used. There remain then, white, carmine, and two purples (violet, “dark blue”). When white was crossed with either of these, Nobbe says the colour becomes paler, whichever sort gave the pollen. Nobbe does not state that he crossed carmine with the purples.
(2) Professor Weldon gives no qualification in his version. Nobbe however states that he found it very difficult to distinguish the result of crossing carmine with white from that obtained by crossing dark blue or violet with white[130], thereby nullifying Professor Weldon’s statement that in every case the cross was a simple mixture of the parental colours—a proposition sufficiently disproved by Miss Saunders’ elaborate experiments.
(3) Lately the champion of the “importance of small variations,” Professor Weldon now prefers to treat the distinctions between established varieties as negligible fluctuations instead of specific phenomena[131]. Therefore when Correns using “yellowish white” obtained one result and Nobbe using “white” obtained another, Professor Weldon hurries to the conclusion that the results are comparable and therefore contradictory. Correns however though calling his flowers gelblich-weiss is careful to state that they are described by Haage and Schmidt (the seed-men) as “schwefel-gelb” or sulphur-yellow. The topics Professor Weldon treats are so numerous that we cannot fairly expect him to be personally acquainted with all; still had he looked at Stocks before writing, or even at the literature relating to them, he would have easily seen that these yellow Stocks are a thoroughly distinct form[132]; and in accordance with this fact it would be surprising if they had not a distinctive behaviour in their crosses. To use our own terminology their colour character depends almost certainly on a compound allelomorph. Consequently there is no evidence of contradiction in the results, and appeal to ancestry is as unnecessary as futile.
2. Datura. As for the evidence on Datura, I must refer the reader again to the experiments set forth in our Report.
The phenomena obey the ordinary Mendelian rules with accuracy. There are (as almost always where discontinuous variation is concerned) occasional cases of “mosaics,” a phenomenon which has nothing to do with “ancestry.”
3. Colours of Rats and Mice. Professor Weldon reserves his collection of evidence on this subject for the last. In it we reach an indisputable contribution to the discussion—a reference to Crampe’s papers, which together constitute without doubt the best evidence yet published, respecting colour-heredity in an animal. So far as I have discovered, the only previous reference to these memoirs is that of Ritzema Bos[133], who alludes to them in a consideration of the alleged deterioration due to in-breeding.
Now Crampe through a long period of years made an exhaustive study of the peculiarities of the colour-forms of Rats, white, black, grey and their piebalds, as exhibited in Heredity.
Till the appearance of Professor Weldon’s article Crampe’s work was unknown to me, and all students of Heredity owe him a debt for putting it into general circulation. My attention had however been called by Dr Correns to the interesting results obtained by von Guaita, experimenting with crosses originally made between albino mice and piebald Japanese waltzing mice. This paper also gives full details of an elaborate investigation admirably carried out and recorded.
In the light of modern knowledge both these two researches furnish material of the most convincing character demonstrating the Mendelian principles. It would be a useful task to go over the evidence they contain and rearrange it in illustration of the laws now perceived. To do this here is manifestly impossible, and it must suffice to point out that the albino is a simple recessive in both cases (the waltzing character in mice being also a recessive), and that the “wild grey” form is one of the commonest heterozygotes—there appearing, like the yellow cotyledon-colour of peas, in either of two capacities, i.e. as a pure form, or as the heterozygote form of one or more combinations[134].