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INFLUENCE OF POLLEN ON THE APPEARANCE OF SEED.

FEW facts in vegetable physiology are more remarkable than the well-ascertained influence of the pollen of one species or variety on the seed and fruit of another species or variety whilst still attached to the female plant. There are several old accounts, and the case has been well proved by Gärtner of the colour of the pea in one variety of the Garden Pea, being changed by the direct action of the pollen of another differently-coloured variety.¹ So, again, the famous St. Valery Apple tree produces many different kinds of fruit, according to the nature of the pollen used; for the singularly-constructed flowers yield no pollen, and they are annually fertilised by a party of French girls, who bring pollen from other trees, and mark with ribbons the flowers thus fertilised.² About a year ago Mr. Beaton gave an analagous case, far more remarkable than any hitherto recorded, for he showed (if my memory does not deceive me) that the pollen of one species acted on the footstalk of the seed-capsule of another species, and caused it slowly to assume a position which it would not otherwise have acquired.³ I forget the name of the plant, and have vainly spent an hour in trying to find the passage, though I am sure I marked it. Will Mr. Beaton have the kindness to repeat the statement? and I am sure it is worth repetition. If he grant this favour, will he inform us whether his observations were made on several flowers, and during one or more years? I remember some difficulty in finding the name of the plant in such catalogues as I happened to have at hand, which led me to suppose that it had, like too many plants, more names than one.⁴—CHARLES DARWIN.

[Beaton's response was printed immediately beneath Darwin's letter:]

(In answering Mr. Darwin's question, allow me, first, to clear myself of any participation in his opening remark, that "Few facts in vegetable physiology are more remarkable than the well-ascertained influence of the pollen of one species or variety on the seed and fruit of another species or variety while still attached to the female plant." Gärtner never proved that—he only asserted it; and when he was pushed to the proof, he lowered his sails, made a second edition of his great work, and confessed many of his errors.

The most practical cross-breeder who has yet appeared has stated "Gärtner's report of the cross-bred seed he has obtained, to be nothing but a mere enumeration of the crosses he has tried to obtain." And with regard to very many of the cases of impregnation mentioned by Gärtner, he, the said cross-breeder, otherwise Dr. Herbert, "utterly repudiates the probability of such impregnation;" and well he might.

It was not Gärtner, but Dr. Wiegman, in 1823, who first said he found the Pea changed colour from being planted along with Vicia sativa, or common Vetch; and Gärtner, two years subsequently, said he caused the same change by means of the pollen; and our Mr. Knight was somewhat smitten with that doctrine.

I had a commission to work over, again and again, every experiment mentioned by Gärtner, Wiegman, and Lageret, and I found over and over again each experiment was without a base. Others proved the same, but it remained for the late Professor Henslow to prove by scientific investigation that the pollen has no visible effect on the seed impregnated; and no cross-breeder of any practice in England at the present day would like to have his name associated with that of Gärtner, for or against any exploit in crossing. Nevertheless, I am firmly of the opinion that Gärtner was right in his belief of the way impregnation is effected.

I forget the plant I mentioned last year as having the penduncle, or stalk, of the flower affected by pollen. Of all the plants I recollect having mentioned, for the last twelve months, there are only five genera that are affected that way—Corbularia and Hermione among the Narcissi, and Erodium, Pelargonium, and Geranium, in that class of plants. The best generic distinction for upholding Corbularia and Hermione as distinct from the true Narcissi, is that the peduncle rises slowly from a horizontal to an upright posture as the seeds ripen in the pod. The Erodiums and a section of Pelargoniums, with, I believe, all the true Geraniums, have the peduncle affected differently from the great mass of Pelargoniums.

It is probable, however, that Mr. Darwin has been thinking of

¹ Gärtner 1849, pp. 80-7. See Correspondence vol. 11, pp. 90-1 and appendix V.

² See Variation 1: 350 and 401.

³ Beaton 1860.

⁴ See Beaton's responses in Correspondence vol. 11, appendix V.

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what was said on the different stages of impregnation at page 330, of Vol. XXVII., the part for this time last year. And I think Gärtner's idea of how the pollen acts is proved both by the Erodiums, including Pelargonium, which is not a natural genus, and the true Geraniums, inasmuch as the footstalk of each flower in all that mass of Donald Beaton 733 species, and in their endless varieties, is the first part that is affected by the pollen. Indeed, I am quite certain of that, for I had at least ten thousand proofs of it. But let me explain.

Take any of the true species out of all the Geraniaceae, cut off the stigma before the pollen can intrude, and the peduncle of that flower will retain its original or natural posture till it decays. A Tom Thumb, or any of the bedders, will prove that very shortly. Take another flower in the same truss, and cross it with the pollen of another species which you know will not cross with it, and the peduncle will turn to the opposite of its natural posture, and will never regain the true position, but the ultimately, as the process of fertilisation went no farther than to affect the footstalk. The next stage is the quickening of the pod, the next that of the lobes of the seeds, and all this may be, and yet no life be given to the embryo of the seeds.

Early next May any one may influence a hundred flowers of the Scarlet Defiance Geranium as far as the footstalk of its flowers, but no farther. Every flower of that one kind which is crossed by its own pollen, or by foreign pollen, will, in eight or ten hours, reverse the posture of the footstalks; but the seedpod is not reached by the contents of the pollen, and the consequence is no seed and no rising of the peduncle. There are many seedlings which will prove the same as Defiance at the end of October, and through November.

Notwithstanding these facts, one can conceive a state of climate which would render the effect of that same pollen active through the three or four stages of impregnation, and produce fertile seed from Defiance. Indeed, the pollen of some kinds or varieties, which will only affect the footstalk very early and very late in the season, will effect a cross in the middle of July; and I have obtained, and I believe I am the only one who has done so, a real cross from Scarlet Defiance, which is over fifteen years old; but I may be mistaken. The case of Cybister, or "The Tumbler" Nosegay Geranium, is a different sport altogether, the truss comes naturally in a reversed position, and takes from three weeks to a month to make a right round change of position.—D. Beaton.)