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Darwin Correspondence Project

From Benjamin Clarke   25 March 1867

2 Mount Vernon | Hampstead N.W.

March 25/67.

Dear Sir,

Please accept my best thanks for the very liberal manner in which you have patronised my forthcoming work1 & as you take so much interest, which I am glad to find, in my experiments on wheat I enclose four ears from the plants to which I referred in my note two of the red & two of the white as they had not been destroyed having kept them among my specimens.2

The experiment with the red wheat appears quite satisfactory;—the two ears grew on the same plant, one of them being cut off before or at the time of flowering & consequently has no seeds. I find it is more depauperated at the upper part than I described it, the flowers being abortive & it must have been precisely in the same condition before it emerged from its sheath. The other is 6-set3 in the first spikelet the two largest grains having been taken out, & I feel sure the depauperated one would from the size of the flowers have been 4- or 5-set.

I think I distinctly recollect ears of white wheat more congested at the upper part than the two I have sent, but these being the largest the others were cut away,—the upper part of one of them has been broken off which has in some degree altered its appearance;—3 or 4 of the spikelets are 7-set, but the uppermost grains are small.

While writing the short account I sent you a suggestion occurred to me which I think will interest you. Supposing the male inflorescence of Zea Mays were all removed as soon as it could possibly be got at by pressing open the sheath, & the female flowers fertilized by pollen from another plant & this operation repeated year after year, there would it appears to me probably be produced in 5 or 6 years, a variety of Indian Corn with only a very few male flowers.4 The consequence of this would most probably be, that the quantity of female flowers & consequently seed, would be increased by a third or nearly doubled, & if so the increased produce of the plant might, in such a country as the United States, amount perhaps to a million annually, or even more as the annual imports into this country are over three millions of quarters;—in 1863 the computed value of the imports was over £4.000.000. Why should not Indian Corn be as docile under the pruning knife as Red Wheat is?

Farmers would have no difficulty in trying the experiment. They could set apart a field for seed to sow again & remove the flowers (as early as possible) from every other plant in a row, year after year. The vigour of the male flowers might, by gardeners be increased, by breaking off all the smaller ones as soon as possible,—of course not cutting off the spikes of females. Doubtless you have a Green House & your gardener could very well attend to the directions given. In looking at Indian Corn it used to occur to me that it was misfortune that it produced so many male flowers at the expense it seemed to me of the quantity of seed produced.

I beg to enclose a note on Hemp5 which I believe will interest you. Being the son of an agriculturist I am naturally interested in Turnips & believe I have discovered a remedy for the Turnip Fly,6 which consists in sowing three kinds of seed, one naked as usual, one covered with thick gum & one covered with resin varnish;—the seeds are thrown into flour so that they do not stick together while drying;—the covered seeds do not come up till after a heavy rain & then would grow so fast that they would escape the Fly, so I am assured by a farmer.

I did not see the nectarine on a peach tree,—it was advertised as exhibited at one of the shows of the R.H.S. at Kensington.7

The Elm referred to is a tree growing on the left hand side on a green just before you come to the Heath, being 20 or 30 yards I should think from the road side, & stands on the south side of a large green mound surrounded with iron railings, which is the Water Company’s reservoir very recently established.8 The arm being out of reach I could not procure any leaves. There is no appearance of disease & it may be 3 or 4 inches in diameter. As a small tree it would be more oramental than the common Elms.

If you have an opportunity of writing a few lines of favourable review for my botanical work which you have received, its sale may be accelerated.9 I relinquished the practice of the medical profession some time since in consequence of the injuries my health had sustained.10 I have the pleasure of seeing your name on the list of contributors to the Royal Society Relief Fund for £100,11 a practical proof of your readiness to assist literary men who have met with reverses.

I remain dear Sir, | Yours very truly | Benjn. Clarke.

Charles Darwin Esqe.

P.S. Should you wish to send any of my communications to any Journal accompanied with some comments of your own you are perfectly at liberty to do so.12 The ears of corn are sent in hope you may make some use of them & therefore need not be returned,—I have taken out all the grains I want. They were grown in rather large flowerpots in rich earth & daily care taken with regard to moisture.

I suppose that if the male flowers were removed from one plant of Indian corn & the females from another so as to make it diœcious either a gigantic or more productive variety would result.


On varieties of Cannabis sativa produced by Pruning.—

Suggestions for the improvement of Turnips

A few years since I grew a female plant of Cannabis in a rather large flower pot with rich mould, taking daily care to keep it in good condition as to moisture, for the purpose of ascertaining whether it would produce embryos by parthogenesis.13 As well as I can recollect it produced seeds 1 or 2 in most of the axils of each pair of leaves but certainly none on the branches. I then cut about the upper third or half of the main stem off to see what the effect would be as to the production of seed. The upper branches then bore several seeds, but this was not satisfactory as regards parthogenesis because a male Hemp plant about that time began to flower.

However notwithstanding the uncertainty about the seeds produced after the male plant flowered, I sowed the seed & in the third generation somewhere about one third of the seeds, perhaps 6 or 7 of them, produced tricotyledonous plants14 the pruning having been continued. Selecting one of these to raise it turned out to produce regularly 3 leaves in a whorl.

I also reared from the same parcel of seed two other female plants but whether they had two or three cotyledons I do not recollect but I well recollect that they had leaves opposite in pairs as Hemp usually grows. Both these plants proved to be monœcious, one of them producing two well developed male flowers, having anthers large as usual, in the axils of the first pair of leaves, & the other, one male flower also in the axil of one of the first leaves.15 These male flowers appeared to me more surprising than the tricotyledonous embryos.

One inference deduced from this this experiment is that the production of seed by the aid of pruning would have the same effects on the generality of plants, as the cultivation of Wild Wheat (Ægilops) & Wild Oats has on those cereals. I have long entertained this view & often wished I knew a Turnip seed grower (a class of men who are known to give every attention to the selection of their plants) that I might explain to him my proposition for improving Turnips, expecting that bulbs two or three times the usual size could soon be produced, differing from ordinary Turnips as the Shaddock does from the Orange.

My proposition is, that as soon as all the flowers become sufficiently distinct so that it may be guessed which will be the largest, all the smaller ones up to 9 out of 10 or 19 out of 20 should be broken off, & the remaining 10th. or 20th. be allowed to flower & fruit. The experiment might be carried still further by cutting away the stamens of the flowers on the lower branches & the ovaries of those on the upper part of the inflorescence as soon as it was practicable to do it. The pollen of the upper flowers would then fall on the ovaries of those beneath them, the juices of which would not be exhausted, or rather lessened, by the production of anthers, at least not to the usual extent.

If Beet continues to be cultivated in France for the manufacture of sugar such an improvement would be still more desirable.16


Clarke refers to his proposed new work, On systematic botany and zoology (Clarke 1870; see letter from Benjamin Clarke, 12 March 1867 and n. 2).
For a description of Clarke’s experiment, see the letter from Benjamin Clarke, 12 March 1867.
Clarke refers to the number of grains in the spikelet.
Zea mays is monoecious, with male flowers located at the top of the stalk, while female flowers are grouped together lower down on an ear or cob (Mangelsdorf 1974, pp. 4–5). In Variation 1: 320–3, CD discussed variability in maize, noting the occurrence both of male flowers among female and more rarely of female flowers among male, as well as reports of hermaphrodite flowers.
Cannabis sativa (see enclosure).
The insect commonly referred to as turnip fly was Haltica nemorum (now Phyllotreta nemorum), a beetle of the family Chrysomelidae that feeds on the young leaves of the turnip (EB 9th ed.).
In the enclosure to his letter of 12 March 1867, Clarke had mentioned a nectarine produced on a peach tree. CD evidently asked for the source of this report in his reply to Clarke’s letter, which has not been found. The report of the tree exhibited at a Royal Horticultural Society show in Kensington has not been found.
In the enclosure to his letter of 12 March 1867, Clarke described an elm tree, with anomalous leaves on one branch, that he saw in Hampstead Heath, north-west London. The West Middlesex Water Company was responsible for the water supply in this area (Post Office London directory 1867).
CD had recently bought a copy of Clarke 1866 (see letter from Benjamin Clarke, 12 March 1867, n. 1). No review of the work by CD was published.
Although he trained as a physician at Winchester, Clarke practised for only a few months (Journal of Botany 28 (1890): 84).
The Royal Society Scientific Relief Fund was set up in 1859; funds were raised by subscription (Record of the Royal Society of London).
CD did not send the notices Clarke enclosed in this letter or the letter of 12 March 1867 to any journal.
Cannabis sativa is a dioecious plant of the family Cannabaceae (Mabberley 1997). Parthenogenesis has not been reported in the species, which is wind-pollinated (Bócsa and Karus 1998).
Cannabis sativa is normally dicotyledonous.
Monoecious varieties of Cannabis sativa have the same flower structure as the normal dioecious plants but the location of the inflorescences is different (Bócsa and Karus 1998, p. 35).
For the development of the sugar beet (Beta vulgaris) in France, see Winner 1993, pp. 15–18.


Clarke, Benjamin. 1870. On systematic botany and zoology, including a new arrangement of phanerogamous plants, with especial reference to relative position, and their relations with the cryptogamous; and a new arrangement of the classes of zoology. London: n.p.

EB 9th ed.: The Encyclopaedia Britannica: a dictionary of arts, sciences, and general literature. 9th edition. 24 vols. and index. Edinburgh: A. and C. Black. 1875–89.

Mabberley, David J. 1997. The plant-book. A portable dictionary of the vascular plants. 2d edition. Cambridge: Cambridge University Press.

Mangelsdorf, Paul C. 1974. Corn. Its origin, evolution, and improvement. Cambridge, Mass.: Belknap Press of Harvard University Press.

Post Office London directory: Post-Office annual directory. … A list of the principal merchants, traders of eminence, &c. in the cities of London and Westminster, the borough of Southwark, and parts adjacent … general and special information relating to the Post Office. Post Office London directory. London: His Majesty’s Postmaster-General [and others]. 1802–1967.

Record of the Royal Society of London: The record of the Royal Society of London for the promotion of natural knowledge. 4th edition. London: Royal Society. 1940.

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

Winner, Christian. 1993. History of the crop. In The sugar beet crop: science into practice, edited by David A. Cooke and R. Keith Scott. London: Chapman & Hall.


Thanks for subscription.

Reports experiments with wheat.

Sends notes on producing varieties by pruning.

Letter details

Letter no.
Benjamin Clarke
Charles Robert Darwin
Sent from
Source of text
DAR 161: 157, 159
Physical description
6pp encl 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 5460,” accessed on 7 December 2021,

Also published in The Correspondence of Charles Darwin, vol. 15