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Darwin Correspondence Project

From Benjamin Clarke   12 March 1867

2 Mount Vernon | Hampstead | N.W.

March 12 67.

Dear Sir,

I have for a long time had in view the addition, to my work on the Natural System of Botany,1 of a new arrangement of the Classes of Zoology on principles closely analogous to those of the botanical Tables of that work, so as to combine the two systems into one system of Botany & Zoology.

By this combination I hope & even expect that they will materially assist in proving each other correct & also explain each other & so facilitate to students the study of both, there being many students in the present time who are initiated in Botany & Zoology nearly at the same time.

The Table of the new arrangement of the Classes of Zoology is now ready for the press & I write to request the favour of your subscription for the work with the zoological addition the price of which to those who have subscribed for the botanical work, & therefore to you, will be only s10/– & you will receive it carriage free.

The botanical part of the work is the same as that you have already received but the book will have a different title i.e. On Systematic Botany & Zoology & will contain 2 or 3 pages of letterpress or possibly more explanatory of the Zoological Table & also 1 or 2 pages of botanical Addenda.2 The botanical Addenda will I believe materially assist in proving the botanical arrangement, especially as regards the flowering plants, to be correct.

Dr. Gray of the British Museum3 & other Zoologists will favour me with their opinions of the Zoological Table before it is printed off.

The botanical arrangement I have every reason to believe is quite successful, especially in its principles, & I have not heard of a single objection to it, so I am encouraged to proceed.4

I beg to enclose a notice of progressive development believing it will interest you. It is presented as an addendum to the Tables in which progressive development is the leading principle, although there is no notice of that subject in the letterpress of the work.5

I remain dear Sir | truly yours | Benjn. Clarke.

Charles Darwin Esqe.


On a mode of producing Varieties by Pruning.

About eight years since I commenced two experiments one on red wheat & the other on white for the purpose of producing a six-set variety, i.e. six grains in a spikelet, three or four being the usual number in cornfields.6 Before the plants flowered all the stems were cut away except one & as soon as the ear was protruded the upper half was cut off, & all the fresh shoots at the base of the stems were removed about once a week or fortnight till the ears were ripened.

The result was that the six-set was produced & in the third year a seven-set spikelet, which as far as I know has not been observed by agriculturists & it seemed very probable that eight-set could be produced.

The experiment which had only economical purposes in view was then discontinued because it was found that cutting off the upper half of the ear for only three years had the very singular effect of occasioning the upper half of the ear in the red wheat to be nearly barren & shrivelled, & of converting the upper half of that in the white into an unnaturally dense spike approaching that of Phalaris Canariensis;7 it was in this that the seven-set was produced. Would not this account for varieties with short spikes? A plant growing in barren ground would have unusually short spikes which in time might perhaps become a permanent variety.

One suggestion may be interesting. If the central bud of a Sun-flower were cut off when the plant was about a foot high, & those of the lateral branches which sprouted afterwards when they became a few inches long & the plant was then left to flower, I quite expect that a corymbous8 variety of the Sun-flower would be produced having many small heads in the place of one, which could be propagated by seed, & the corymbs increased in density by continuing the pruning.

This leads to the inference that progressive development depends in great measure on the condition of the parents at the time of fertilization;— whatever that condition may be it is unalterably stamped on the offspring. But it appears to me that this is not the only cause of progressive development. Spontaneous generation although it has been regarded as unphilosophical is nevertheless it appears to me rendered most probable by Dactylium oogenum,9 & if so it is in all probability a very common occurrence. This being the case, spontaneous alteration at the time of generation, not depending on the condition of the parents, would perhaps be a phenomenon not so unlikely to occur as otherwise might be supposed. The production of a nectarine on a peach tree I regard as an instance of this spontaneous alteration,10 & at Hampstead there is an Elm tree one arm of which has an apparently different leaf, I think considerably smaller, & much denser branches than the rest of the tree, which I suppose to arise from one of the buds having spontaneously a new mode of growth.11

If then buds at the time of generation can take on a new mode of growth, of course embryos can do the same, & here we should have a prolific source of new varieties.

I therefore attribute progressive development to two causes which act either separately, or, not improbably, sometimes in conjunction.


Clarke refers to A new arrangement of phanerogamous plants (Clarke 1866), a taxonomic work in which Clarke presented a natural system of botanical classification based on the position of the ovaries. Although CD’s name does not appear on the list of original subscribers to the privately published work (see Clarke 1866), he evidently bought a copy; he recorded a payment in his Account books–cash account (Down House MS) of £1 under the heading ‘Botanical book Clarke’ for 26 December 1866. CD’s copy has not been found.
Clarke’s new work, On systematic botany and zoology, was published in 1870 (Clarke 1870); CD recorded a payment in his Account books–cash account (Down House MS) of 10s. under the heading ‘Syst. Bot. & Zooly B. Clarke’ for 20 October 1870. CD’s copy is in the Darwin Library–Down.
Clarke refers to John Edward Gray, who was the keeper of the zoological collections at the British Museum.
For CD’s view on the lack of criticism of Clarke 1866, see the letter to J. D. Hooker 17 March [1867].
The tables in Clarke 1870 are arranged to show a genealogical relationship among the different classes, but this relationship is not noted in the accompanying text.
Red and white wheat are varieties of Triticum aestivum, common bread-wheat (Peterson 1965, p. 15).
The reference is to Phalaris canariensis or canary grass, which has spike-like panicles that resemble those of club wheat (Triticum compactum).
Corymbous: i.e. corymbose.
Dactylium oogenum is a species of anamorphic fungus (that is, a fungus persisting in an asexual state). Clarke evidently believed its occurrence was the result of spontaneous generation. On the Victorian debates over spontaneous generation, see Strick 2000.
CD noted in Variation 1: 340 that there was considerable evidence of peach trees producing nectarines by bud-variation. CD defined bud-variation as including ‘all those sudden changes in structure or appearance’ that occasionally occurred ‘in full-grown plants in their flower-buds or leaf-buds’ (Variation 1: 373).
In Variation 1: 390–4, CD considered certain cases of bud-variations that gave rise to different forms of growth on a single plant as consequences of reversion.


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.

Peterson, Rudolph Frederick. 1965. Wheat: botany, cultivation and utilization. London: L. Hill Books. New York: Interscience Publishers.

Strick, James. 2000. Sparks of life: Darwinism and the Victorian debates over spontaneous generation. Cambridge, Mass.: Harvard University Press.

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


Requests CD’s subscription to his On systematic botany and zoology [1870]. "Progressive development" is a leading principle of his work.

Letter details

Letter no.
Benjamin Clarke
Charles Robert Darwin
Sent from
Source of text
DAR 161: 157/1, 158
Physical description
4pp encl 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 5439,” accessed on 23 September 2021,

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