Part 32

This is of course on account of the maternal seed characters. Unless the coat-characters are treated separately from the cotyledon-characters Laxton’s description is very accurate. Both this and the statements respecting the “shape” of the seeds, a term which as used by Laxton means much more than merely “wrinkled” and “smooth,” are recognizably true as general statements.

Separation of hypallelomorphs.

Here Professor Weldon’s quotation ceases. It is unfortunate he did not read on into the very next sentence with which the paragraph concludes:--

“These sports appear to become fixed and permanent in the next and succeeding generations; and the tendency to revert and sport thenceforth seems to become checked if not absolutely stopped.”

The combinations being exhausted. Perhaps Professor Weldon thought his authority was here lapsing into palpable nonsense!

Now if Professor Weldon instead of leaving off on the word “ancestry” had noticed this passage, I think his article would never have been written.

Laxton proceeds:--

“The experiments also tend to show that the height of the plant is singularly influenced by crossing; a cross between two dwarf peas, commonly producing some dwarf and some tall [? in the second generation]; but on the other hand, a cross between two tall peas does not exhibit a tendency to diminution in height.

“No perceptible difference appears to result from reversing the parents; the influence of the pollen of each parent at the climax or fourth generation producing similar results.”

Laxton constantly refers to this conception of the “climax” of--as we now perceive--analytical variation and recombination. Many citations could be given respecting his views on this “climax” (cp. p. 167).

The significance of this latter testimony I will presently discuss.

Professor Weldon next appeals to a later paper of Laxton’s published in 1890. From it he quotes this passage:

“By means, however, of cross-fertilisation alone, and unless it be followed by careful and continuous selection, the labours of the cross-breeder, instead of benefiting the gardener, may lead to utter confusion,”

Here again the reader would have gained had Professor Weldon, instead of leaving off at the comma, gone on to the end of the paragraph, which proceeds thus:--

“because, as I have previously stated, the Pea under ordinary conditions is much given to sporting and reversion, for when two dissimilar old or fixed varieties have been cross-fertilised, three or four generations at least must, under the most favourable circumstances, elapse before the progeny will become fixed or settled; and from one such cross I have no doubt that, by sowing every individual Pea produced during the three or four generations, hundreds of different varieties may be obtained; but as might be expected, I have found that where the two varieties desired to be intercrossed are unfixed, confusion will become confounded, and the variations continue through many generations, the number at length being utterly incalculable.”

Further subdivision and recombination of hypallelomorphs.

Professor Weldon declares that Laxton’s “experience was altogether different from that of Mendel.” The reader will bear in mind that when Laxton speaks of fixing a variety he is not thinking particularly of seed-characters, but of all the complex characters, fertility, size, flavour, season of maturity, hardiness, etc., which go to make a serviceable pea. Considered carefully, Laxton’s testimony is so closely in accord with Mendelian expectation that I can imagine no chance description in non-Mendelian language more accurately stating the phenomena.

Here we are told in unmistakable terms the breaking up of the original combination of characters on crossing, their re-arrangement, that at the fourth or fifth generation the possibilities of sporting [sub-division of compound allelomorphs and re-combinations of them?] are exhausted, that there are then definite forms which if selected are thenceforth fixed [produced by union of similar gametes?] that it takes longer to select some forms [dominants?] than others [recessives?], that there may be “mule” forms or forms which cannot be fixed at all [produced by union of dissimilar gametes?].

For instance the talls produced by crossing dwarfs are such “mules.” Tschermak found in certain cases distinct increase in height in such a case, though not always (p. 531).

“The remarkably fine but unfixable pea Evolution.” Laxton, p. 37.

But Laxton tells us more than this. He shows us that numbers of varieties may be obtained--hundreds--“incalculable numbers.” Here too if Professor Weldon had followed Mendel with even moderate care he would have found the secret. For in dealing with the crosses of Phaseolus Mendel clearly forecasts the conception of compound characters themselves again consisting of definite units, all of which may be separated and re-combined in the possible combinations, laying for us the foundation of the new science of Analytical Biology.

How did Professor Weldon, after reading Mendel, fail to perceive these principles permeating Laxton’s facts? Laxton must have seen the very things that Mendel saw, and had he with his other gifts combined that penetration which detects a great principle hidden in the thin mist of “exceptions,” we should have been able to claim for him that honour which must ever be Mendel’s in the history of discovery.

When Laxton speaks of selection and the need for it, he means, what the raiser of new varieties almost always means, the selection of definite forms, not impalpable fluctuations. When he says that without selection there will be utter confusion, he means--to use Mendelian terms--that the plant which shows the desired combination of characters must be chosen and bred from, and that if this be not done the grower will have endless combinations mixed together in his stock. If however such a selection be made in the fourth or fifth generation the breeder may very possibly have got a fixed form--namely, one that will breed true. On the other hand he may light on one that does not breed true, and in the latter case it may be that the particular type he has chosen is not represented in the gametes and will never breed true, though selected to the end of time. Of all this Mendel has given us the simple and final account.

Apart from fresh original variations, and perhaps in some cases imperfect homozygosis of some hypallelomorphs.

At Messrs Sutton and Sons, to whom I am most grateful for unlimited opportunities of study, I have seen exactly such a case as this. For many years Messrs Sutton have been engaged in developing new strains of the Chinese Primrose (Primula sinensis, hort.). Some thirty thoroughly distinct and striking varieties (not counting the Stellata or “Star” section) have already been produced which breed true or very nearly so. In 1899 Messrs Sutton called my attention to a strain known as “Giant Lavender,” a particularly fine form with pale magenta or lavender flowers, telling me that it had never become fixed. On examination it appeared that self-fertilised seed saved from this variety gave some magenta-reds, some lavenders, and some which are white on opening but tinge with very faint pink as the flower matures.

On counting these three forms in two successive years the following figures appeared. Two separately bred batches raised from “Giant Lavender” were counted in each year.

Magenta Lavender White red faintly tinged

1901 1st batch 19 27 14 " 2nd " 9 20 9 1902 1st " 12 23 11 " 2nd " 14 26 11 -- -- -- 54 96 45