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Letter 4021

Scott, John to Darwin, C. R.

3 Mar 1863

    Summary Add

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    JS criticises natural selection as based on an innate "continuously watchful selective principle".

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    Seeks seed of wild Rocky Mountain maize.

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    What is CD's view on origin of maize?

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    Seeks information on self-sterility of Passiflora and Lobelia.

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    Weeping habit of trees.

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    Intended to say bisexual plants presented more established varieties than unisexual, not that they are more variable.

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    Explains his opinion that homomorphically fertilised Primula will produce only their own form. Is trying homomorphic crosses with different coloured Primula varieties.

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    Asks to read Asa Gray's 2d review of Orchids.

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    Has finally successfully fertilised Gongora, but it was done by unnatural means.

Transcription

Botanic Gardens Edinburgh

March. 3d. 1863.

Sir.

I am glad to hear that the variation of Imatophyllum, will be of service to you. I was afraid that it might be of too short a standing for your noticing. It is certainly a very striking one, and may perhaps be the origin of a remarkably distinct race. I will be glad to afford every particular regarding it, you desire.

I have been endeavouring to get seeds of the wild Maize, which occurs on the Rocky Mountains; from description it appears to be remarkably distinct from any cultivated form. Crosses with the latter might afford most interesting results: Do you regard it as the parent of the numerous forms now in cultivation? I suppose it has only as yet been found wild in the New World. I am daily expecting a selection of the most dissimilar varieties grown by Barr & Sugden. So with those you have favoured me with, I will have a variety of subjects to work upon. I am very desirous, however, for the wild form, but I know not where to get it. I have searched the University Herbarium here, but it does not contain a single fertile specimen.

Are the Passifloras mentioned by you in Origin, invariably sterile when treat with `own-pollen'; or is it a local occurrence? P. quadrangularis, for example, fruits freely in some hot-houses, in others, though flowering most profusely it obstinately refuses to fruit. In our gardens a form perhaps a variety of the former called Bonapartea will not set a single fruit. It may, however, be otherwise in another locality: Will you be so kind as favour me with the names of any perfectly sterile species, with ``own-pollen''.? as I find that some of the species I had thought to be sterile are only locally so,: If such could be rendered fertile by application of pollen from other species, would they be of any service to you? I would much like a little information on these points; as I am working somewhat blindly: I have had yet little experience. I have the same difficulties with Lobelia: I have made your desire known to Mr. Mc.Nab. He informs me that he has already communicated all the information he could gather on weeping-trees; & inheritance of character from seeds, to M. Neuman of the Jardin des Plantes; who he supposes will shortly publish on the subject. I do not think, however, from what I have heard him saying, that he has had much practical experience in these matters; his remarks, will I believe principally be founded on the experience of others. What the results may be I know not   I am rather inclined to think they will be of a negative nature   So far as I can ascertain—from the large experience of some of the nursery foremen here—the character rarely if ever—appears amongst the seedlings.

I did not mean to say that bisexual plants are more variable than unisexual, all that I intended, was, that the former presented a greater number of naturally established varieties, than the latter. This I believe, to be a consequence of the more intimate relation of the sexual organs: as affording a better chance for these being imbued with similar formative tendencies, than occur in the unisexual arrangement. This opinion I hold partly on the grounds that similar variations will rarely appear in a number of individuals at any given time— much more frequently variations will be peculiar to individuals, or even portions of such will be originally representative: and thus in unisexual plants, the embryo must necessarily in general be the resultant of organs imbued with dissimilar formative tendencies—the normal specific, & a diverging form. This combination then causing as it does an immediate change in the conditions originating the latter forms and acting upon the most susceptible stages of the organism; will as I believe, cause an immediate reversion in the embryonic resultant, to the normal specifical form. This I think is fully supported by the results of crossing hybrids—incipient forms—with one or other of their original parents, established forms—as we see by a few successive crosses the other form entirely eliminated. Considering then the results from crossing of hybrids—which be it remembered are products of well established forms—what may we expect from such in the case of accidental variations versus the normal forms. Again, considering the truly casual agencies employed by Nature for effecting fertilisation in the vegetable kingdom; I really, candidly speaking, find great difficulty in understanding how species can possibly be manufactured by an innate, continuously watchful, selective principle. There seems to me a necessity for admitting the occasional actions of a superinduced power to explain the establishment of new forms of vegetative life. The struggle for existence, does not I think fully meet the difficulty—more especially as applied to annuals—inasmuch as the strongest individuals may be continually fertilised by the weaker, and thus constantly check the domination of their progeny. Again supposing individual utility alone, as the great end striven after by Nature in the metamorphosis of organic beings; why should there necessarily be a dependence between the internal structure & external form?

The great morphological differences of the sexual forms of Catasetum, for example, seem to me—though I may be quite wrong—scarcely consistent with a mere regard to specific utility. Is it not highly probable that in their native wilds, different insects will visit the different forms: and thus somewhat frustrate the plans of Nature. Does the occasional occurrence of the three sexual forms of Catasetum on one spike, not oppose the view that these forms were attained by a gradual modification? On the latter view, ought we not to have expected intermediate forms only? The metamorphosis you mention in Orchid Book on the authority of Mr. Rodgers is most remarkable; more especially if we are right in regarding the hermaphrodite Myanthus as the original progenitor? Such an occurrence seemingly disproves what I hinted at in my last regarding Acropera, still no variation having ever been observed in the latter indicates a morphological status which may justify us in anticipating a homomorphic progeny.

I have thus hurriedly and imperfectly attempted to lay before you a few of the difficulties, which have presented themselves to me, while considering species as products of Natural Selection; these & kindred points I have taken up in my paper. But I know not whether I will yet have made my view sufficiently clear; I fail so completely in expressing myself: as I would like. I hope you will excuse me for troubling you with this subject as after all I may be quite wrong—though it has engaged me now for sometime.

In respect to the opinion that homomorphically fertilised Primulas, will produce their own-form only—I may remark that it occurred to me when I first considered the bearings of these plants upon my views. Since: I have examined the different forms very carefully, and I find in concordance with your observations—that the two forms are most decidedly permanent. I have seen what, I suppose may be a similar case to that referred to by you on the authority of Mr. Wooler: viz, a long-styled variety of P. vulgaris, producing in early spring a number of short-styled flowers. But—mark—there was no change in the position of the stamens: these as far as my observations go are always permanent. From this permanency then I at once concluded as above; having a firm conviction that established seed-variations, will always produce their own characters only, when kept pure: this I anticipate as the result of Vegetable Parthenogenesis—when satisfactorily established. Some of the Cryptogams may be already mentioned as producing female forms only by parthenogenesis, e.g. certain Mosses & Chara. I thus regard Primula & Acropera as parallel cases: I would expect different results from Catasetum &c where individuals still produce the different forms. I do not believe that the relative lengths of stamens & pistils in the two forms of Primula could have been attained if these had been fertilised by other than own-form pollen. I am inclined to suppose that they even yet under cultivation, might be caused to revert by continuous crossing of the two forms. P. Sinensis is a case in point—which you first drew my attention to—being regularly raised from seed: and here we find pretty frequently a form with stamens & pistils equal. These points, I likewise consider in my paper. I may mention that I have raised long-styled plants of P. cortusoides only from own-form pollen. As I had little seed however, I raised only a few plants, consequently I could lay no particular stress on the experiment.

However, I thought I had evidence of such from varieties of P. vulgaris in the gardens here: there being beds of these plants—all of which are long-styled. I thought, therefore that they must have been propagated by seed. I have now asked Mr. Mc.Nab their history and he informs me that have been merely propagated by division. I have, however, a few seedlings of different forms of Primula all homomorphically fertilised—I expect some of these will be in flower shortly, and afford us some more information on this point.

I am trying at present homomorphic crosses, with different coloured flowers of Primula vulgaris &c. I am following out your hints likewise on decreased fertility between varieties presenting only variation in colour, it may perhaps be a more common occurrence than is supposed. I will be much obliged if you favour me with a perusal of Asa Gray's 2d. review of Orchid Book. I will return it immediately. I am busy at present with a Bletia; I have at last been perfectly successful in my attempts to fertilise Gongora—it is by forced & unnatural work however—I have no less than fourteen capsules on a single spike swelling beautifully—I could almost have wished that it had been otherwise. I will give you particulars when I write again, as I fear I will have already exhausted your time and patience.

I remain | Sir | Yours very respectfully | J. Scott

    Footnotes Add

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    f1 4021.f1
    See letter to John Scott, 16 February [1863] and n. 6.
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    f2 4021.f2
    In his letters to Scott of 11 December [1862] and 19 December [1862] (Correspondence vol. 10), CD suggested that he repeat the experiments first conducted by Karl Friedrich von G¨artner on the degree of cross and hybrid sterility exhibited by differently coloured varieties of maize (see G¨artner 1844 and 1849). CD had subsequently sent, with his letter to Scott of 16 February [1863], seed of a cultivated variety of maize provided by Asa Gray.
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    f3 4021.f3
    Barr & Sugden was a firm of London nurserymen with premises at 12 King Street, Covent Garden.
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    f4 4021.f4
    Scott refers to CD's discussion in Origin, pp. 250--1, of plants that could be `far more easily fertilised by the pollen of another and distinct species, than by their own pollen'. At CD's suggestion, Scott decided to carry out additional experiments on sterility and hybridisation in Passiflora (see Correspondence vol. 10, letter from John Scott, 17 December [1862]); he published his results in Scott 1864d.
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    f5 4021.f5
    In his letter to Scott of 19 November [1862] (Correspondence vol. 10), CD mentioned that plants of the genus Lobelia were `more easily fertilised' by the pollen of another species than by their own pollen. See also Origin, pp. 250--1.
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    f6 4021.f6
    In his letter to Scott of 16 February [1863], CD asked Scott to pass on a request for information concerning the inheritance of the weeping habit in trees to James McNab, curator of the Royal Botanic Garden, Edinburgh.
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    f7 4021.f7
    In Variation 2: 18--19, CD cited Verlot 1865 as the source for McNab's observations on the inheritance of the weeping character in birch and beech trees. The essay by Bernard Verlot, Louis Neumann's colleague at the Jardin des Plantes in Paris, won the prize in the open competition of the Soci´et´e Imp´eriale et Centrale d'Horticulture for 1862, and first appeared in the society's journal (Verlot 1864). There is an annotated copy of Verlot 1865 in the Darwin Library--CUL (see Marginalia 1: 817--19).
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    f8 4021.f8
    In his letter to Scott of 21 January [1863], CD asked for clarification of Scott's views concerning the relationship between the form of reproduction and the heritability of variation in ferns. Scott's reply has not been found; however, it apparently included a more general discussion of the relationship between reproduction and inheritance in plants (see letter to John Scott, 16 February [1863] and n. 12). For an account of Scott's views on this subject, see the letter from John Scott, 16 January 1863, n. 11. By `bisexual' Scott meant `hermaphrodite' (that is, bearing both male and female reproductive parts in the same flower), and by `unisexual' he meant `diclinous' (that is, bearing male and female reproductive parts in different flowers, whether on the same or different plants).
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    f9 4021.f9
    Scott first raised this objection to natural selection, based upon blending inheritance, in his letter to CD of 6 December [1862] (Correspondence vol. 10). For CD's response, see the letter to John Scott, 6 March 1863.
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    f10 4021.f10
    In Orchids, pp. 236--47, CD established that the orchid species Catasetum tridentatum had hermaphrodite and female forms so different from the male as to have been assigned to different genera (Myanthus barbatus and Monachanthus viridis, respectively).
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    f11 4021.f11
    Scott refers to the case, reported to CD by John Rogers and cited in Orchids, p. 236 n., of an orchid that one year produced flowers characteristic of Myanthus barbatus, and the following year produced those characteristic of Catasetum tridentatum. See Correspondence vol. 10, letter from John Rogers, 22 January 1862.
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    f12 4021.f12
    See letter from John Scott, 18 February [1863].
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    f13 4021.f13
    In a missing letter, Scott had evidently informed CD that he was preparing a paper on the relationship between the form of reproduction and the heritability of variation in plants (see letter to John Scott, 16 February [1863] and n. 12). This subject had been Scott's main focus for some time (see n. 8, above, and letter from John Scott, 16 January 1863 and n. 11); however, the planned paper was apparently never published.
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    f14 4021.f14
    See letter from John Scott, 18 February [1863], and letter to John Scott, 20 [February 1863].
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    f15 4021.f15
    CD cited William Alexander Wooler's case of polyanthuses that produced long-styled flowers late, but not early, in the season in `Dimorphic condition in Primula', p. 79 (Collected papers 2: 47).
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    f16 4021.f16
    On Scott's interest in vegetable parthenogenesis, see Scott 1862a and Correspondence vol. 10, letters from John Scott, 15 November [1862] and 17 December [1862]. CD was also interested in the analogy between parthenogenetic plants producing only female offspring and long-styled Primula sinensis producing only long-styled offspring when homomorphically fertilised (see Correspondence vol. 10, letter to John Scott, 11 December [1862], and this volume, letter to John Scott, 20 [February 1863]).
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    f17 4021.f17
    See Correspondence vol. 10, letter to John Scott, 3 December [1862], and letter from John Scott, 6 December [1862].
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    f18 4021.f18
    See n. 13, above.
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    f19 4021.f19
    Scott experimented extensively with species of Primula during 1863, and, at CD's prompting, wrote a paper on the subject (Scott 1864a; see letters from John Scott, 21 May [1863], [3 June 1863], and 23 July [1863]).
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    f20 4021.f20
    See letter from John Scott, 23 July [1863], and Scott 1864a, pp. 97--103.
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    f21 4021.f21
    Scott refers to CD's discussion in Origin, pp. 270--1, of G¨artner's experiments on maize, in which two differently coloured varieties of the same species were found to be infertile together, and his experiments on Verbascum, in which crosses between differently coloured varieties of the same or of different species were found to be less fertile than the parallel crosses between similarly coloured varieties. CD had encouraged Scott to attempt these and similar experiments in his letters of 19 November [1862] and 11 December [1862] (Correspondence vol. 10); he reiterated the point about differently coloured varieties of maize in his letters to Scott of 21 January [1863] and 16 February [1863].
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    f22 4021.f22
    A. Gray 1862a. See letter to John Scott, 16 February [1863] and n. 5.
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    f23 4021.f23
    See letter from John Scott, 21 March [1863].
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    f24 4021.f24
    See letter from John Scott, 6 January 1863, and letter to John Scott, 16 February [1863].
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    f25 4021.f25
    See letter from John Scott, 21 March [1863].
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