Part 30

We are still far from understanding maternal seed-form--and perhaps size--as a dominant character. So far, as Miss Saunders has pointed out to me, it appears to be correlated with a thick and coloured seed-coat.

* * * * *

We have now seen the nature of Professor Weldon’s collection of contradictory evidence concerning dominance in peas. He tells us: “Enough has been said to show the grave discrepancy between the evidence afforded by Mendel’s experiments and that obtained by observers equally trustworthy.”

He proceeds to a discussion of the Telephone and Telegraph group and recites facts, which I do not doubt for a moment, showing that in this group of peas--which have unquestionably been more or less “blend” or “mosaic” forms from their beginning--the “laws of dominance and segregation” do not hold. Professor Weldon’s collection of the facts relating to Telephone, &c. has distinct value, and it is the chief addition he makes to our knowledge of these phenomena. The merit however of this addition is diminished by the erroneous conclusion drawn from it, as will be shown hereafter. Meanwhile the reader who has studied what has been written above on the general questions of stability, “purity,” and “universal” dominance, will easily be able to estimate the significance of these phenomena and their applicability to Mendel’s hypotheses.

D. Miscellaneous cases in other plants and animals.

Professor Weldon proceeds:

“In order to emphasize the need that the ancestry of the parents, used in crossing, should be considered in discussing the results of a cross, it may be well to give one or two more examples of fundamental inconsistency between different competent observers.”

The “one or two” run to three, viz. Stocks (hoariness and colour); Datura (character of fruits and colour of flowers); and lastly colours of Rats and Mice. Each of these subjects, as it happens, has been referred to in the forthcoming paper by Miss Saunders and myself. Datura and Matthiola have been subjected to several years’ experiment and I venture to refer the reader who desires to see whether the facts are or are not in accord with Mendel’s expectation and how far there is “fundamental inconsistency” amongst them to a perusal of our work.

But as Professor Weldon refers to some points that have not been explicitly dealt with there, it will be safer to make each clear as we proceed.

1. Stocks (Matthiola). Professor Weldon quotes Correns’ observation that glabrous Stocks crossed with hoary gave offspring all hoary, while Trevor Clarke thus obtained some hoary and some glabrous. As there are some twenty different sorts of Stocks it is not surprising that different observers should have chanced on different materials and obtained different results. Miss Saunders has investigated laws of heredity in Stocks on a large scale and an account of her results is included in our forthcoming Report. Here it must suffice to say that the cross hoary ♀ × glabrous ♂ always gave offspring all hoary except once: that the cross glabrous ♀ × hoary ♂ of several types gave all hoary; but the same cross using other hoary types did frequently give a mixture, some of the offspring being hoary, others glabrous. Professor Weldon might immediately decide that here was the hoped for phenomenon of “reversed” dominance, due to ancestry, but here again that hypothesis is excluded. For the glabrous (recessive) cross-breds were pure, and produced on self-fertilisation glabrous plants only, being in fact, almost beyond question, “false hybrids” (see p. 34), a specific phenomenon which has nothing to do with the question of dominance.

The number in Haage and Schmidt’s list exceeds 200, counting colour-varieties.

Professor Weldon next suggests that there is discrepancy between the observations as to flower-colour. He tells us that Correns found violet Stocks crossed with “yellowish white” gave violet or shades of violet flaked together. According to Professor Weldon

“On the other hand Nobbe crossed a number of varieties of M. annua in which the flowers were white, violet, carmine-coloured, crimson or dark blue. These were crossed in various ways, and before a cross was made the colour of each parent was matched by a mixture of dry powdered colours which was preserved. In every case the hybrid flower was of an intermediate colour, which could be matched by mixing the powders which recorded the parental colours. The proportions in which the powders were mixed are not given in each case, but it is clear that the colours blended.”

The original passage is in Landwirths. Versuchstationen, 1888, XXXV. [not XXXIV.], p. 151.

On comparing Professor Weldon’s version with the originals we find the missing explanations. Having served some apprenticeship to the breeding of Stocks, we, here, are perhaps in a better position to take the points, but it is to me perfectly inexplicable how in such a simple matter as this he can have gone wrong.

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, 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.

“Es ist sogar sehr schwierig, einen Unterschied in der Farbe der Kreuzungsprodukte von Karmin und Weiss gegenüber Dunkelblau oder Violett und Weiss zu erkennen.”

(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. 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; 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.

See also the case of Buchsbaum, p. 146, which received similar treatment.

One of the peculiarities of most double “sulphur” races is that the singles they throw are white. See Vilmorin, Fleurs de pleine Terre, 1866, p. 354, note. In Wien. Ill. Gartenztg. 1891, p. 74, mention is made of a new race with singles also “sulphur,” cp. Gartenztg. 1884, p. 46. Messrs Haage and Schmidt have kindly written to me that this new race has the alleged property, but that six other yellow races (two distinct colours) throw their singles white.

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, who alludes to them in a consideration of the alleged deterioration due to in-breeding.

Biol. Cblt. XIV. 1894, p. 79.

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.