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Darwin Correspondence Project

To Thomas Rivers   1 February [1863]1

Down. | Bromley. | Kent. S.E.

Feb. 1st

My dear Sir

I can answer your query on much higher authority than any observations which I could make in months of time.2 The “stomata” or mouths, which by their lips have power of opening & closing, & which when opened put the spaces within the leaf into free communication with the open air, are far more abundant on the lower than on the upper surface of leaf.— “More commonly there are few or none on the upper side.”3 In the white lily it has been calculated that there are in square inch of surface, 60,000 stomata on lower surface, & only 3,000 on upper surface; in the apple there are 24,000 to the inch: in some plants 170,000 to the square inch.!4

I have often marvelled over the American type of features.—5

I was heartily glad to see your handwriting, for I was meditating a query: I am taking “Weeping trees”, as an example how inexplicable the laws of inheritance are; some weeping trees reproducing themselves almost truly by seed, & some quite failing to do so.—

Can you give me any certain facts on character of seedlings from a weeping trees?6

Also have you ever sowed from a sporting branch or bud (i.e. case of bud-variation) & if so what was result:—7 I know case of Boston Nectarine.—8

My dear Sir | Yours sincerely | Ch. Darwin

If no answer, I will understand no facts.—


The year is established by the relationship between this letter and the letter from Thomas Rivers, 30 January 1863.
In his letter of 30 January 1863, Rivers asked CD to confirm his observation that the ‘lungs’ of plants were situated on the under-surface of the leaves. CD refers to Asa Gray (see nn. 3 and 4, below).
CD’s information on stomata was taken from Gray’s First lessons in botany and vegetable physiology, an annotated copy of which is in the Darwin Library–CUL (A. Gray 1857; see Marginalia 1: 347). Gray’s observation, ‘More commonly there are few or none on the upper side’ continued, ‘direct sunshine evidently being unfavorable to their operation’ (A. Gray 1857, p. 157).
CD quoted the figures from A. Gray 1857, pp. 156–7.
In his letter to CD of 30 January 1863, Rivers discussed the effects of soil and climate on the North American population.
In chapter 12 of Variation, CD cited the weeping habit of trees as an example of ‘how feeble, capricious, or deficient the power of inheritance sometimes is’ (Variation 2: 17), the weeping habit being transmitted to the seedlings sometimes strongly and sometimes feebly. Rivers provided CD with the ‘crowning case’ of the vagaries of inheritance in trees with his information on varieties of weeping ash (Variation 2: 19).
By the term ‘bud-variation’, CD meant ‘all those sudden changes in structure or appearance which occasionally occur in full-grown plants in their flower-buds or leaf-buds’ (Variation 1: 373). CD made several inquiries on the subject of bud-variation in December 1862 (see Correspondence vol. 10, letter to John Scott, 19 December [1862], letter to Thomas Rivers, 23 December [1862], and letter to Hugh Falconer, 29 December [1862]). Rivers was able to provide CD with several examples of bud-variations, including cases where fully grown peach trees had suddenly produced nectarines and vice versa (Variation 1: 340), purple plums had produced yellow plums (Variation 1: 375), and various rose varieties produced other varieties (Variation 1: 380–1, 409–10).
The Boston nectarine was reported to have been produced from a peach stone, and to have produced by seed a closely allied nectarine. CD cites Knight 1826, p. 394, and Downing 1845, p. 502, on this point in Variation 1: 340.


Answers TR’s query about stomata.

CD will use "weeping trees" as an example of how inexplicable the laws of inheritance are, and asks for facts on character of seedlings.

Letter details

Letter no.
Charles Robert Darwin
Thomas Rivers
Sent from
Source of text
Sotheby’s, London (23–4 July 1987)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 3962,” accessed on 30 April 2017,

Also published in The Correspondence of Charles Darwin, vol. 11