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Darwin Correspondence Project

To Asa Gray   7 December 1870

Down. | Beckenham | Kent. S.E.

Dec 7. 1870

My dear Gray

I have been very glad to receive yr letter this mg—1 I have for some time been wishing to write to you, but have been half worked to death in correcting my uncouth English for my new book—2 I have been glad to hear of yr cases appearing like incipient dimorphism. I believe that they are due to mere variability, & have no significance. I found a good instance in Nolana prostrata, & experimented on it, but the forms did not differ in fertility.3 So it was with Amsinckia of which you told me.4 I have long thought that such variations afforded the basis for the development of dimorphism. I was not aware of such cases in Phlox, but have often admired the arrangement of the anthers, causing them to be all raked by an inserted proboscis. I am glad also to hear of your curious case of variability in ovules &c.

I said that I had been wishing to write to you, & this was about yr Drosera, which after many fluctuations between life & death, at last made a shoot, which I cd observe.5 The case is rather interesting; but I must first remind you that the filament of Dionæa is not sensitive to very light prolonged pressure, or to nitrogenous matter, but is exquisitely sensitive to the slightest touch. In our Droseræ the filaments are not sensitive to a slight touch, but are sensitive to prolonged pressure from the smallest object of any nature; they are also sensitive to solid or fluid nitrogenous matter. Now in yr Drosera the filaments are not sensitive to a rough touch or to any pressure from non-nitrogenous matter, but are sensitive to solid or fluid nitrogenous matter. Is it not curious that there shd be such diversified sensitiveness in allied plants?6

I recd a very obliging letter from Mr Morgan, but did not see him, as I think he said he was going to start at once for the continent.7 I am sorry to hear rather a poor account of Mrs Gray to whom my wife I both beg to be very kindly remembered—8

My dear Gray | Yours affectionately | Ch Darwin


CD was correcting the proof-sheets of Descent.
See letter to J. D. Hooker, [13 June 1870?] and n. 3. Nolana prostrata is now N. humifusa.
See Correspondence vol. 11, letter to Asa Gray, 20 March [1863] and n. 19; CD refers to Amsinckia spectabilis.
Gray had sent CD bulbs of Drosera filiformis (the threadleaf sundew) from Kew in 1869, advising him to see whether he could detect any sensitivity in the glandular hairs; see Correspondence vol. 17, letters from Asa Gray, 20 October 1869 and 26 and 29 October [1869].
See Insectivorous plants, pp. 19–37.
CD refers to Lewis Henry Morgan. See letter from L. H. Morgan, 9 August 1870, and letter to L. H. Morgan, 11 August [1870].
CD refers to Jane Loring Gray.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Insectivorous plants. By Charles Darwin. London: John Murray. 1875.


Believes AG’s cases of incipient dimorphism are due to mere variability. Has found examples in Nolana and Amsinckia; believes such variation is the basis for the development of dimorphism. Was unaware of variations in Phlox.

Sensitivity of Drosera and Dionaea.

Letter details

Letter no.
Charles Robert Darwin
Asa Gray
Sent from
Source of text
Gray Herbarium of Harvard University (90)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 7388,” accessed on 16 June 2021,

Also published in The Correspondence of Charles Darwin, vol. 18