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Darwin Correspondence Project

From J. D. Hooker   14 August 1873

Royal Gardens Kew

Aug 14th/73

Dear Darwin

Strachey has been in the North, & has just written to say that he will gladly accept for Saturday 23d.—1

I have often speculated on the point you allude to, which is specially conspicuous in the Nelumbium.2 Ferns & various Cryptogams do not show it as Phaenogams do.3 It is not conspicuous in other water plants as in Nelumbium which further holds its leaves high above the water, but for this association of the two means of getting out of the way as it were of injury from water, I should have supposed that both waxy coat & hairs were connected with absorption or respiratory functions.— I have lately wondered whether both may not subserve some purpose connected with Actinic or chemical rays of the Sun, especially as the waxy secretion is often more conspicuous on the upper leaf-surface—

The prevalence of indumentum on the under surface however points to transpiration in some cases; in others perhaps it is a provision against the attacks of insects, which harbor on under surfaces.

I can quite fancy water impeding both the actinic & calorific effects of sun-light on the leaf. We find watering most prejudicial in the hot sun. It is a splendid subject for experiments.4

Adam is a good man I believe, business-like & considerate— I hear that D. Galton is a thousand times worse than Ayrton & utterly detested in the office.5

The rehabilitating Ayrton with the Judge Advocacy, a sinecure suppressed by this very Ministry, is the jolliest job I have heard of for many a long day.—6

I will see to Oxalis at once7

Ever affec yours | Jos D Hooker

CD annotations

1.1 Strachey … 23d.— 1.2] crossed pencil
2.6 I … leaf-surface— 2.9] ‘Noadded red crayon
5.1 Adam … day.— 6.2] crossed pencil


See letter to J. D. Hooker, 13 August 1873 and n. 2. CD had noted that leaves and fruit were often protected by fine hairs or a waxy coating. Nelumbium (now Nelumbo) is the lotus genus.
Cryptogamia (non-flowering) and Phanerogamia (flowering) were former divisions of plants.
For a summary of contemporary research on plant hairs (trichomes) and cuticular waxes, see Sachs 1873, pp. 85–8.
See letter to J. D. Hooker, 13 August 1873 and n. 4. Acton Smee Ayrton was the former first commissioner of works, William Patrick Adam his successor; Douglas Strutt Galton was director of public works and buildings in the Office of Works (ODNB).
Ayrton had been appointed judge-advocate-general (ODNB).
See letter to J. D. Hooker, 13 August 1873 and n. 3. The reference is to Oxalis sensitiva (a synonym of Biophytum sensitivum).


ODNB: Oxford dictionary of national biography: from the earliest times to the year 2000. (Revised edition.) Edited by H. C. G. Matthew and Brian Harrison. 60 vols. and index. Oxford: Oxford University Press. 2004.


Has observed CD’s points. Except for leaves of Nelumbium, would have supposed both wax and hairs were connected with absorption or respiratory functions. May subserve some function connected with rays of sun. Watering most prejudicial in the hot sun: a splendid subject for experiments.

Adam is a good man.

Letter details

Letter no.
Joseph Dalton Hooker
Charles Robert Darwin
Sent from
Source of text
DAR 103: 167–8
Physical description
ALS 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 9011,” accessed on 26 March 2023,

Also published in The Correspondence of Charles Darwin, vol. 21