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Darwin Correspondence Project

To Asa Gray   26[–7] November [1862]1

Down Bromley Kent

Nov. 26th

My dear Gray

The very day after my last letter yours of Novr. 10th & the Review in Silliman, which I feared might have been lost, reached me.2 We were all very much interested by the political part of your letter: in some odd way one never feels that information & opinions printed in a newspaper come from a living source; they seem dead, whereas all that you write is full of life.— Many thanks for P.S. about maize; if the husked form had been the aboriginal, it would surely have not varied so readily; there must be some mistake in statement of Indian, quoted by Aug. St. Hilaire.—3 The Reviews interested me profoundly;4 you rashly ask for my opinion & you must consequently endure a long letter.

First for Dimorphism:5 I do not at present like the term “Diœcio-dimorphism”; for I think it gives quite false notion, that the phenomena are connected with a separation of the sexes.6 Certainly in Primula there is unequal fertility in the two forms, & I suspect this is case with Linum; & therefore I felt bound in Primula paper to state that it might be a step towards dioicous condition;7 though I believe there are no dioicous forms in Primulaceæ or Linaceæ. But the three forms in Lythrum convince me that the phenomenon is in no way necessarily connected with any tendency to separation of sexes.8 The case seems to me in result or function to be almost identical with what old C. K. Sprengel called “dichogamy”,9 & which is so frequent in truly hermaphrodite groups; namely the pollen & stigma of each flower being mature at different periods. If I am right it is very advisable not to use term “diœcious” as this at once brings notion of separation of sexes.— I hope you will be able to attend a little to Plantago; I can hardly understand the sentence in your article.10 In which form does stigma project in bud (this occurs in long-styled Lythrum, but is not then fertilised)?11 is the short-styled (i.e. your long-stamened) really sterile? You will think that I am in the most unpleasant, contradictory, fractious humour, when I tell you that I do not like your term of “precocious fertilisation” for your second class of dimorphism.12 If I can trust my memory, the state of corolla, of stigma & pollen-grains is different from state of parts in bud; that they are in a condition of special modification. But upon my life I am ashamed of myself to differ so much from my betters on this head.— The temporary theory which I have formed on this class of Dimorphism, just to guide experiment, is that the perfect flowers can only be perfectly fertilised by insects & are in this case abundantly crossed; but that the flowers are not always, especially in early spring, visited enough by insects, & therefore the little imperfect self-fertilising flowers are developed to ensure a sufficiency of seed for present generations.13 Viola canina is sterile, when not visited by insects, but when so visited forms plenty of seed.14 I infer from structure of 3 or 4 forms of Balsamineæ that these require insects; at least there is almost as plain adaptation to insects as in Orchids.—15 I have Oxalis acetosella ready in pots for experiment next spring;16 & I fear this will upset my little theory; unless I can as Hooker says “Oh you will wriggle out of anything”.—17 Campanula carpathica, as I proved this summer, is absolutely sterile if insects are excluded. Specularia speculum is fairly fertile when enclosed; & this seemed to me to be effected by the frequent closing of the flower; the inward angular folds of corolla corresponding with the clefts of the open stigma, & in this action pushing pollen from outside of stigma on to its surface.18 Now can you tell me, does Spec. perfoliata close its flower like S. speculum with angular inward folds; if so, I am smashed without some fearful “wriggling”.— Are the imperfect flowers of your Specularia the early or the later ones? very early or very late? It is rather pretty to see importance of closing of flowers of Sp. speculum.—19

I entirely agree with you in your remarks on the part which crossing plays.20 I was much perplexed by Oliver’s remarks in N. Hist Review of the Primula case, on the lower plants having sexes more often separated than in the higher plants,—so exactly the reverse of what takes place in animals.—21 Hooker in Review of Orchids repeats this remark.22 There seems to me much truth in what you say, & it did not occur to me, about no improbability of specilisation in certain lines in lowly organised beings. I could hardly doubt that the Hermaphroditic state is the aboriginal one. But how is it in the conjugation of Confervæ—is not one of the two individuals here in fact male & the other female??23 I have been much puzzled by this contrast in sexual arrangements between plants & animals. Can there be anything in following consideration. By roughest calculation about 13 of British genera of aquatic plants belong to Linnean classes of Mono- & Diœcia; whilst of terrestrial plants (the aquatic genera being substracted) only 113 of genera belong to these two classes. Is there any truth in this fact generally? Can aquatic plants, being confined to a small area or small community of individuals, require more free crossing & therefore have separate sexes?

But to return to one point; does not Alph. Decandolle say that aquatic plants taken as a whole are lowly organised compared with terrestrial;24 & may not Oliver’s remark on separation of sexes in lowly organised plants stand in some relation to their being frequently aquatic? Or is this all rubbish?

I have left myself little room for orchids & indeed I have little to say except to express my admiration at clearness & ingenuity with which you explain & describe all the forms.25 It seems to me all excellently done, & has interested me beyond measure.— Do your Platantheras smell sweetest at night; this I suspect is clear guide that moths are the fertilisers.— I have been especially interested by case of P. psycodes, more especially since the D. of Argyll’s contemptuous remarks on my case of Angræcum, which in action seems analogous to your case.26

But by far the most wonderful is the case of G. tridentata; I hope you will confirm so remarkable a physiological fact.27 If I understand rightly the rostellum alone is penetrated,—the part primordially of a stigmatic nature. In this observation you have anticipated an experiment, which I mean to try, whether pollen-tubes will penetrate the great rostellum of Cattleya.—28 I daresay you are quite right about self-fertilisation being much commoner than I thought with orchids.29 Did I tell you that I have found in Neottia nidus avis that this ensues, if in course of few days the flowers are not visited by insects.?30

Your observations on Cypripedium seem excellent; & I daresay I am wholly wrong;31 it seems to me now more likely that small insects should lick juice off hairs with jaws or short proboscis, than with long proboscis. How curious about the little bristles on the stigma! What a magnificent compliment you end your Review with!32 You & Hooker seem determined to turn my head with conceit & vanity (if not already turned) & make me an unbearable wretch.—

With most cordial thanks, my good & kind friend | Farewell | C. Darwin

P.S. | In my last letter, I mentioned Bates’ paper:33 he is a man of lowly origin, of great force of character, & wonderfully self-educated, but constitutionally of low spirits & poor & under unpleasant circumstances of life. Could you induce any of your Zoological co-editors, just to notice his paper (& if so inform me);34 it would be a good & charitable deed, for it would encourage & please a man, that wants & deserves encouragement.

What a fearfully long letter I have written!

P.S. 2d. Would you be so kind as to tell me whether Fragaria vesca & Virginiana differ much Botanically for I cannot make out that any one has succeeded in crossing them.—35

I have just had long letter from Hooker on part which crossing plays in Nature; I must consider it well, & see if it alters my notions.—36


The year is established by the relationship to the letter from Asa Gray, 10 November 1862. CD refers in his second postscript to having received the letter from J. D. Hooker, 26 November 1862; since Joseph Dalton Hooker’s letter could not have arrived at Down before 27 November 1862, the second postscript must have been added on the latter date. From Gray’s reply (see letter from Asa Gray, 9 December 1862), it appears that this letter was sent in the same envelope as the letter to Asa Gray, 23 November [1862]; however, since the two letters have separate salutations and valedictions, they have been treated separately.
In his letter of 10 November 1862, Gray had enclosed proof-sheets of a portion of the November 1862 number of the American Journal of Science and Arts (commonly known as ‘Silliman’s journal’, after its founder Benjamin Silliman), which included Gray’s follow-up article to his review of Orchids (A. Gray 1862b). See also letter to Asa Gray, 23 November [1862].
CD refers to a postscript to the letter from Asa Gray, 10 November 1862, that is now missing. In his letter of 16 October [1862], CD had asked Gray about a report that, under cultivation, the bracts of wild maize had been found to decrease in size. CD here refers to the claim of a young Guarany Indian, reported by Auguste Saint-Hilaire, that Zea mays grew wild in the humid forests of his native Paraguay (A. de Candolle 1855, 2: 951). In Variation 1: 320–1, CD stated: A peculiar kind [of maize], in which the grains, instead of being naked, are concealed by husks as much as eleven times in length, has been stated on insufficient evidence to grow wild in Brazil. It is almost certain that the aboriginal form would have had its grains thus protected; but the seeds of the Brazilian variety produce, as I hear from Professor Asa Gray, and as is stated in two published accounts, either common or husked maize; and it is not credible that a wild species, when first cultivated, should vary so quickly and in so great a degree.
See n. 2, above. In addition to A. Gray 1862b, the November 1862 number of the American Journal of Science and Arts included A. Gray 1862e (see n. 5, below).
A. Gray 1862e.
The phenomenon now known as heterostyly, the occurrence of which CD had described in his paper ‘Dimorphic condition in Primula, had earlier been termed ‘dioecio-dimorphism’ by Gray and John Torrey (Torrey and Gray 1838–43, 2: 38–9). See also letters from Asa Gray, [10 July 1860] (Correspondence vol. 8) and 11 October 1861 (Correspondence vol. 9). Gray used the term in his discussion of dimorphism in the American Journal of Science and Arts (A. Gray 1862e, p. 419).
‘Dimorphic condition in Primula, p. 95 (Collected papers 2: 61–2). In the conclusion to his later paper, ‘Two forms in species of Linum, p. 83 (Collected papers 2: 105), CD stated: That in some cases this dimorphism may be a step towards a complete separation of the sexes, I will not dispute; but good reasons could be assigned to show that there is no necessary connexion between reciprocal dimorphism and a tendency to dioecious structure. Although good is gained by the inevitable crossing of the dimorphic flowers, yet numerous other analogous facts lead me to conclude that some other quite unknown law of nature is here dimly indicated to us.
In ‘Three forms of Lythrum salicaria, which was read before the Linnean Society on 16 June 1864, CD stated: As some authors consider reciprocal dimorphism to be the first stage toward dioeciousness, the difficulty of understanding how a trimorphic plant like Lythrum salicaria could become dioecious should be noticed; and as dimorphism and trimorphism are so closely allied, it is not probable that either state is necessarily in any way related to a separation of the sexes—though it may occasionally lead to this end.
C. K. Sprengel 1793. CD’s heavily annotated copy of this work is in the Darwin Library–CUL (Marginalia 1: 774–85).
In A. Gray 1862e, p. 419, Gray stated that two principal kinds of dimorphism had been noticed by botanists. The first of these, he noted, he had called ‘diœcio-dimorphism’ (now called heterostyly). Before discussing the second kind, which he called ‘precocious fertilization’ (now called cleistogamy), he commented: The diœcio-dimorphous species of Plantago had seemed to confuse this case with the next. That is, the short-stamened flowers appeared to be fertilized in the closed flower, and the long-stamened and generally sterile plants therefore to be generally useless … a recent observation on a single specimen … shows the top of the style projecting from the tip of the closed corolla. This refers the case to the same category with Houstonia, Primula, &c. See also letter from Asa Gray, 29 December 1862, and Correspondence vol. 11, letter to Asa Gray, 19 January [1863].
See n. 10, above. See also letter to Asa Gray, 23[–4] July [1862].
CD’s notes of his observations on Viola canina, made in May 1862, are in DAR 111: 3–5. See also letter to J. D. Hooker, 30 May [1862], letter to W. E. Darwin, [31 May 1862], and letter to Asa Gray, 10–20 June [1862]. Gray wrote on CD’s letter ‘But Viola goes on all summer’; see letter from Asa Gray, 29 December 1862.
CD refers to several species of Balsaminaceae sent to him by Hooker in October 1862 (see letter to Daniel Oliver, 13 October [1862], letter to J. D. Hooker, 14 [October 1862], and letter from J. D. Hooker, [18 October 1862]).
See letter to Asa Gray, 10–20 June [1862] and n. 24. CD had cultivated plants of Oxalis acetosella with a view to testing a possible case of heterostyly, but later decided that the species was not heterostyled (see letters to Daniel Oliver, 20 [April 1862] and 24 April [1862], and letter to J. D. Hooker, 30 May [1862]). There are notes on his experiments on the cleistogamic flowers of Oxalis acetosella, made in the spring of 1863, in DAR 109 (ser. 2): 6.
CD’s notes of his observations on Campanula carpathica (a misspelling of C. carpatica) and Specularia speculum, dated 4 October 1862, are in DAR 79: 113. These observations are recorded in Cross and self fertilisation, p. 174.
CD had repeatedly asked Gray for information regarding Specularia speculum since learning from him that it had cleistogamic flowers (see letters from Asa Gray, 11 October 1861 (Correspondence vol. 9), 2–3 July 1862, 18–19 August 1862, and 5 September 1862, and letters to Asa Gray, 10–20 June [1862], 23[–4] July [1862], and [3–]4 September [1862]). CD marked the last three sentences of this paragraph with a marginal line, apparently in order to draw Gray’s attention to his request.
In his review, Gray criticised a point in Daniel Oliver’s anonymous review of CD’s paper, published in the Natural History Review ([Oliver] 1862c). Oliver had referred in his review (p. 236; see also p. 238) to two kinds of dimorphism: one that was ‘apparently favourable to variation, marked primarily by a partial or complete separation of the sexes’ (i.e., heterostyly), and one that was ‘conservative, and unfavourable to variation’, with the sexual organs of certain flowers to some extent enclosed and sealed up (i.e., cleistogamy). In A. Gray 1862e, p. 420, Gray commented: we were somewhat surprised at finding that the reviewer of Darwin’s Primula-paper in the Natural History Review … regards the separation of sexes, and therefore cross-fertilization, as favouring variation, and self-fertilization as necessarily inimical to it. This probably comes from not considering that while close-breeding tends to keep a given form true—in virtue of the ordinary likeness of offspring to parents—it equally and in the same way tends to perpetuate a variation once originated from that form, and also, along with selection (natural or artificial), to educe and further develope or confirm said variety. On the other hand, free cross-breeding of incipient varieties inter se and with their original types is just the way to blend all together, to repress all salient characteristics as fast as the mysterious process of variation originates them, and fuse the whole into a homogeneous form.
In considering the apparent tendency in Primula towards a separation of the sexes, Oliver raised the question ‘why did they ever become hermaphrodite?’ ([Oliver] 1862c, p. 238). He went on to say: While we may … suggest that certain species are tending to a separation of the sexes, we must not forget that arguments may be advanced to shew that it is not impossible but that they may be striving towards more perfect hermaphroditism, especially if we bring to mind the evidence … furnished by the ‘Geological Record.’ This evidence does certainly appear in favour of a greater predominance of unisexual forms at an early period than obtains at the present day. Gray responded to this in A. Gray 1862e, p. 420, stating: on morphological grounds, we should look upon hermaphroditism, rather than the contrary, as the normal or primary condition of flowers, and enquire how and why so many became diclinous … Forms which are low in the scale as respects morphological completeness may be high in the scale of rank founded on specialization of structure and functions. See also letter to Daniel Oliver, 15 April [1862] and n. 3.
[J. D. Hooker] 1862d, p. 371.
CD refers to filamentous green algae.
The reference is probably to A. de Candolle 1855, a heavily annotated copy of which is in the Darwin Library–CUL (see Marginalia 1: 106–53).
CD refers to Gray’s follow-up article to his review of Orchids (A. Gray 1862b), in which he detailed a number of his observations on North American orchid species.
In his article, Gray noted that Platanthera psycodes had a long and curved nectary (A. Gray 1862b, p. 425). In his review of Orchids, George Douglas Campbell, eighth duke of Argyll, had questioned CD’s conclusion that a moth with an unusually long proboscis must be responsible for the pollination of Angraecum sesquipedale, in view of its similarly long nectary ([G. D. Campbell] 1862, pp. 394–5; see Orchids, pp. 197–203).
Gray had introduced his description of Gymnadenia tridentata (a synonym of Platanthera clavellata, the small green wood orchid) with the comment: ‘we hesitate to bring forward our too scanty observations until another summer affords an opportunity to test them’ (A. Gray 1862b, p. 426); he confirmed his observations in A. Gray 1863a, pp. 293–4. See also letters from Asa Gray, 18–19 August 1862 and 22 September 1862. CD made undated notes referring to Gray’s account of this species (DAR 70: 8, 17), and cited Gray’s observations in ‘Fertilization of orchids’, p. 147 (Collected papers 2: 144).
CD suggested to John Scott that he might carry out this experiment on Cattleya, in the letter to John Scott, 3 December [1862].
In Orchids, CD sought to demonstrate that the ‘main object’ of the various ‘contrivances by which Orchids are fertilised’ was to ensure cross-fertilisation. He noted only one exception (p. 359). In A. Gray 1862b, p. 426, Gray repeated his earlier description (A. Gray 1862c, p. 259–60) of the occurrence of self-fertilisation in Platanthera hyperborea and Gymnadenia tridentata, noting: ‘Natura non agit saltatim, and is more flexible and diversified in her ways than we are apt to think: many other cases of occasional or habitual self-fertilization may be expected among Orchids.’ CD included the two species mentioned by Gray on an undated list of ‘self-fertilisers’ that is now in DAR 70: 167, and included a modified discussion of the occurrence of self-pollination in orchids in Orchids 2d ed., pp. 288–93.
Gray concluded his article by expressing his gratitude to CD for ‘having brought back teleological considerations into botany’ (A. Gray 1862b, p. 428). He continued (p. 429): In this fascinating book on the fertilization of Orchids and in his paper explaining the meaning of dimorphism in hermaphrodite flowers, Mr. Darwin,—who does not pretend to be a botanist—has given new eyes to botanists, and inaugurated a new era in the science.
Gray was one of the botanical editors of the American Journal of Science and Arts; Gray reviewed Bates 1862a in the journal in September 1863 (A. Gray 1863b). See also letter from H. W. Bates, 24 November 1862, and letter to H. W. Bates, 25 November [1862].
CD was preparing a draft of the part of Variation dealing with ‘Facts of variation of Plants’ (Variation 1: 305–72; see ‘Journal’ (Correspondence vol. 10, Appendix II)). In his account of strawberries (Variation 1: 351–4), CD noted that the European and American species could be crossed ‘with some difficulty’, but considered it ‘improbable that hybrids sufficiently fertile to be worth cultivation will ever be thus produced.’ He continued (p. 352): ‘This fact is surprising, as these forms structurally are not widely distinct, and are sometimes connected in the districts where they grow wild, as I hear from Professor Asa Gray, by puzzling intermediate forms.’


Bates, Henry Walter. 1862. Contributions to an insect fauna of the Amazon valley. Coleoptera: Longicornes. Annals and Magazine of Natural History 3d ser. 9: 117–24, 396–405, 446–58.

[Campbell, George Douglas.] 1862. [Review of Orchids and other works.] Edinburgh Review 116: 378–97.

Candolle, Alphonse de. 1855. Géographie botanique raisonnée ou exposition des faits principaux et des lois concernant la distribution géographique des plantes de l’époque actuelle. 2 vols. Paris: Victor Mason. Geneva: J. Kessmann.

Collected papers: The collected papers of Charles Darwin. Edited by Paul H. Barrett. 2 vols. Chicago and London: University of Chicago Press. 1977.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Cross and self fertilisation: The effects of cross and self fertilisation in the vegetable kingdom. By Charles Darwin. London: John Murray. 1876.

‘Dimorphic condition in Primula’: On the two forms, or dimorphic condition, in the species of Primula, and on their remarkable sexual relations. By Charles Darwin. [Read 21 November 1861.] Journal of the Proceedings of the Linnean Society (Botany) 6 (1862): 77–96. [Collected papers 2: 45–63.]

‘Fertilization of orchids’: Notes on the fertilization of orchids. By Charles Darwin. Annals and Magazine of Natural History 4th ser. 4 (1869): 141–59. [Collected papers 2: 138–56.]

Marginalia: Charles Darwin’s marginalia. Edited by Mario A. Di Gregorio with the assistance of Nicholas W. Gill. Vol. 1. New York and London: Garland Publishing. 1990.

Orchids 2d ed.: The various contrivances by which orchids are fertilised by insects. By Charles Darwin. 2d edition, revised. London: John Murray. 1877.

Orchids: On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. By Charles Darwin. London: John Murray. 1862.

Sprengel, Christian Konrad. 1793. Das entdeckte Geheimniss der Natur im Bau und in der Befruchtung der Blumen. Berlin: Friedrich Vieweg.

‘Three forms of Lythrum salicaria’: On the sexual relations of the three forms of Lythrum salicaria. By Charles Darwin. [Read 16 June 1864.] Journal of the Linnean Society (Botany) 8 (1865): 169–96. [Collected papers 2: 106–31.]

‘Two forms in species of Linum’: On the existence of two forms, and on their reciprocal sexual relation, in several species of the genus Linum. By Charles Darwin. [Read 5 February 1863.] Journal of the Proceedings of the Linnean Society (Botany) 7 (1864): 69–83. [Collected papers 2: 93–105.]

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Discusses AG’s article ["Dimorphism", Am. J. Sci. 2d ser. 34 (1862): 419–20]. Does not like the terms "dioecio-dimorphism" or "precocious fertilisation". Discusses the separation of sexes in plants; cannot doubt that hermaphroditism is the aboriginal state.

Discusses AG’s observations on orchids and his review of Orchids [Am. J. Sci. 2d ser. 34 (1862): 138–51].

Letter details

Letter no.
Charles Robert Darwin
Asa Gray
Sent from
Source of text
Gray Herbarium of Harvard University (50)
Physical description
ALS 6pp †

Please cite as

Darwin Correspondence Project, “Letter no. 3830,” accessed on 20 June 2024,

Also published in The Correspondence of Charles Darwin, vol. 10