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Darwin Correspondence Project

From J. D. Hooker   28 December 1860


Dec 28 /60

Dear Darwin

Your notes about the little Compos. are very interesting indeed—1 I would certainly send them to G. C. which will woodcut the illustration—2 The case is a great extension of the well-known fact, that many Compositæ (the common groundsel is one)3 have a layer of vesicles full of mucus on the achænium, which swell & burst when wet—& so hold down the seed to ground, but I know of no case like this, of the mucus cells being developed only on the lower sides of the oblique Achænium—4 This side is the outer as respects the position of the floret in the capitulum, & it is a curious fact that various other Compos: with erect (or but slightly inclined) achænia have a similar glandular development on the outer surface only—& especially such as inhabit S. Africa— The Selection principle comes in here capitally—   The laws of growth render all the achænia in most capitula of comp. lop sided, especially such comps. as have the outermost flowers female (the case with all these). in falling it is the lop-side that touches the ground, & the most glandular that adhere best & hence grow &c &c &c.5

The same phenomena occur in seeds (not seed vessels as in Compos.) of Cruciferæ, & it is curious that that genus of Crucif. in which the viscid coat is thickest is Australian. I have followed the subject a little in Crucif.—   Some Crucif. you know have dehiscent fruit: others indehiscent: I find the mucous coat general in the dehiscent—never in the indehiscent.—but some genera have upper half of capsule indehiscent, lower dehiscent. in these all the seeds are mucous, or all not mucous.—   this is only inteligeable on Nat. Select. principle & shews that the simple physiolog. peculiarity of testa is more permanent than structure of Capsule.— this further falls in with my principle of classification of the Order—   What is more odd is that the mucous or dry testa is a more constant character than form & direction of Embryo! I did want to write a good paper on whole subject in reference to classification & origin of genera & species too in order Cruciferæ, but have not strength of mind for it.6

You ask how my Book on plants brews?7—as flat as beer with bad malt.— I have no Torula cerevisiæ 8 in me any more.— I have arrived at a hale old age & shall take care of it. & am seriously thinking of taking out a commission of Lunacy against my one hard working friend Huxley—   I feel all sorts of inward monitors advising me against over excitement or9


CD annotations

3.1 You … or 3.5] crossed ink
Top of first page: ‘Pumilio argyrolepis V. G. Chronicle for my paper p. 5. Jan 5. 1860’10 ink

CD note:11

I think I might describe seeds of Pumilio & say I wondered by what gradation produced— D Groundsel, I suppose no Bladders then how is this?— As achenia becomes more oblique. bladders more developed??—


The paper, a note on the achenes of Pumilo argyrolepis, was sent to the Gardeners’ Chronicle and Agricultural Gazette. It was published in the issue of 5 January 1861. See Correspondence vol. 9, letter to Gardeners’ Chronicle, [before 5 January 1861]. The paper includes two woodcuts of the underside of the mature flower.
Groundsel (Senecio vulgaris) is a common yellow-flowered weed of waste ground.
CD’s paper described the way in which the underside of the fruit (the achenium) is covered by numerous little bladders; when the bladders become damp, they burst and make the seed case sticky, allowing the achenium to rest upright and become firmly attached to an object.
In his paper, CD stated: ‘Whether the tendency of the achenia to place themselves upright be of any service to the plant would be hard to determine; but it seems possible that the salver-shaped calyx, which, as we have seen, so rapidly absorbs moisture and carries it down to the lower surface of the achenia, might aid in utilising dew or showers of fine rain.’ (Collected papers 2: 38).
The plant family Cruciferae was, in Hooker’s time, believed to be a natural family characterised by the pod-like capsules that enclose the seeds and by the shape of the embryo. Nevertheless, the grouping of the smaller divisions and the definition of the genera gave rise to much dispute. Hooker had been interested in the family since his early work on the Kerguelen Land cabbage, a plant that he considered the simplest of all Cruciferae. See Correspondence vol. 4, letter from J. D. Hooker, [c. 4 March 1847].
Torula cerevisiae is the yeast micro-organism that acts in the fermentation of beer.
The diagrams were drawn by CD and enclosed with the letter to Hooker, 26 December [1860]. They are similar to those published in the Gardeners’ Chronicle (Collected papers 2: 37).
Hooker probably supplied CD with the name Pumilo argyrolepis in the missing portion of the letter. The annotation refers to the species whose seeds CD had just described; in the manuscript sent to Hooker, he had called the plant Siloxerus (see letter to J. D. Hooker, 26 December [1860]). CD erred in writing ‘1860’ rather than ‘1861’.
The note is in DAR 100: 145. It was marked ‘CH VIII’ in brown crayon, a reference to chapter 8 of CD’s ‘big book’ on species. In that chapter, entitled ‘Difficulties on the theory of natural selection in relation to passages from form to form’ (Natural selection, pp. 339–86), CD discussed the difficulties associated with supposing gradual transitions in the functional change of organs or parts.


Collected papers: The collected papers of Charles Darwin. Edited by Paul H. Barrett. 2 vols. Chicago and London: University of Chicago Press. 1977.

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

Natural selection: Charles Darwin’s Natural selection: being the second part of his big species book written from 1856 to 1858. Edited by R. C. Stauffer. Cambridge: Cambridge University Press. 1975.


CD’s article worth publishing in Gardeners’ Chronicle. JDH interprets CD’s observation in terms of selection. Has observed similar phenomenon in Cruciferae, where it can be taxonomically important.

Letter details

Letter no.
Joseph Dalton Hooker
Charles Robert Darwin
Sent from
Source of text
DAR 100: 143–4, 146–8
Physical description
†, CD note , 3 CD sketches

Please cite as

Darwin Correspondence Project, “Letter no. 3033,” accessed on 20 October 2021,

Also published in The Correspondence of Charles Darwin, vol. 8