Chapter V: Professor Weldon’s Quotations From Laxton

In support of his conclusions Professor Weldon adduces two passages from Laxton, some of whose testimony we have just considered. This further evidence of Laxton is so important that I reproduce it in full. The first passage, published in 1866, is as follows:--

“The results of experiments in crossing the Pea tend to show that
the colour of the immediate offspring or second generation sometimes
follows that of the female parent, is sometimes intermediate between
that and the male parent, and is sometimes distinct from both; and
although at times it partakes of the colour of the male, it has
not been ascertained by the experimenter ever to follow the exact
colour of the male parent[139]. In shape, the seed frequently has an
intermediate character, but as often follows that of either parent.
In the second generation, in a single pod, the result of a cross
of Peas different in shape and colour, the seeds are sometimes all
intermediate, sometimes represent either or both parents in shape
or colour, and sometimes both colours and characters, with their
intermediates, appear. The results also seem to show that the third
generation or the immediate offspring of a cross, frequently varies
from its parents in a limited manner--usually in one direction
only, but that the fourth generation produces numerous and wider
variations[140]; the seed often reverting partly to the colour and
character of its ancestors of the first generation, partly partaking
of the various intermediate colours and characters, and partly
sporting quite away from any of its ancestry.”

[139] 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.

[140] 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[141].”

[141] 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[142].”

[142] 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[143],
and the variations continue through many generations, the number at
length being utterly incalculable.”

[143] 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[144] or forms which cannot be fixed at all[145] [produced by union of dissimilar gametes?].

[144] 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).

[145] “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[146]. 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.

[146] 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

The numbers 54 : 96 : 45 approach the ratio 1 : 2 : 1 so nearly that there can be no doubt we have here a simple case of Mendelian laws, operating without definite dominance, but rather with blending.

When Laxton speaks of the “remarkably fine but unfixable pea _Evolution_” we now know for the first time exactly what the phenomenon meant. It, like the “Giant Lavender,” was a “mule” form, not represented by germ-cells, and in each year arose by “self-crossing.”

This is only one case among many similar ones seen in the Chinese Primrose. In others there is no doubt that more complex factors are at work, the subdivision of compound characters, and so on. The history of the “Giant Lavender” goes back many years and is not known with sufficient precision for our purposes, but like all these forms it originated from crossings among the old simple colour varieties of _sinensis_.