To Asa Gray 26[–7] November 1
Down Bromley Kent
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 of British genera of aquatic plants belong to Linnean classes of Mono- & Diœcia; whilst of terrestrial plants (the aquatic genera being substracted) only 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
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].
Please cite as
Darwin Correspondence Project, “Letter no. 3830,” accessed on 24 February 2017, http://www.darwinproject.ac.uk/DCP-LETT-3830