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Darwin Correspondence Project

To J. D. Hooker   21 October [1875]1

Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.

Oct. 21st

My dear Hooker

Having as a wonder no letters to write, I am going to amuse myself by scribbling a few lines to you.— Perhaps you wd. like to read enclosed on Gunnera: anyhow it need not be returned.2 I wonder whether the same explanation can apply to odd little flower in middle, or on axis of umbel of Carrot, which has always been a mystery to me.3 By the way a Melastoma (I know not what or whence) has just flowered in my hot-house, but the 2 sets of stamens do not differ except in size: I have however fertilised a few flowers with pollen from both.4

The boys have been observing Stipa, & Horace has made a hygrometer with a bit of the twisted awn or pistil (or whatever it may be) & mounted it on a graduated circle; & I have never in my life been more astonished than at its sensitiveness.5 If you blow gently at it from 1 or 2 feet distance, it absorbs moisture & instantly rotates. It is still more surprising that the moisture from a finger held near, not touching, instantly & repeatedly caused a slight movement of about a degree.— What a strong attraction for water the cells must have! We have been disgusted to find in Watts Dict. of Chemistry that some one has used Stipa as a hygrometer.6

I have been nicely sold: I saw in a Journal that Dr Pfeiffer gigantic Nomenclator Botanicus is now published, & I assumed that it was like Steudel’s with a list of the species & Habitats, so ordered it.7 And now I find it costs £12"s12.0 & that it contains no species,, only genera, & is of not the least use to me or to anyone, except a describer. Would it be real use to Linn. Soc? If so I wd give it to the Soc. or to any poor working Botanist, or I will ask William & Norgate whether they could sell it for 12 price.8 It is folly for me to keep such a book.

Ever yours affecty | C. Darwin


The year is established by the relationship between this letter and the letter from J. D. Hooker, 23 October 1875.
CD enclosed a sheet of the letter from Fritz Müller, 12 September 1875, with Müller’s remarks on terminal flowers in the inflorescence of Gunnera manicata (giant rhubarb).
CD had noted that the central floret in umbels of wild carrot (Daucus carota) was dark purple and different from the others (see Correspondence vol. 9, letter to Journal of Horticulture, [before 18 June 1861], and Correspondence vol. 22, letter to Thomas Meehan, 9 October 1874).
See letter to W. T. Thiselton-Dyer, 3 October [1875] and n. 5. CD was interested in species of the family Melastomaceae (now Melastomataceae) that had flowers with two forms of stamens, differing in both size and colour.
Francis Darwin was studying the ability of some seeds to bury themselves in the ground and had noted the hygroscopic properties of the awns of the seeds (see letter to J. D. Hooker, 13 October [1875] and n. 6, and letter from J. D. Hooker, 14 October 1875 and n. 4). Horace Darwin’s hygrometer is described in F. Darwin 1876c, pp. 155–6. Stipa: needlegrass.
CD’s annotated copy of Henry Watts’s Dictionary of chemistry is in the Darwin Library–Down (see Marginalia 1: 195–6). CD’s copy consists of the first three volumes of the second edition (Watts 1872–4), volumes four and five of an 1871 reprint of the first edition (Watts 1863–8), and a supplement to the first edition dated 1872. See Watts 1872–4, 3: 233, for the reference to the awn of a seed of Stipa being used as a hygrometer.
CD’s copy of Ernst Gottlieb Steudel’s Nomenclator botanicus (Steudel 1841) is in the Darwin Library–CUL. Ludwig Pfeiffer’s Nomenclator botanicus (Pfeiffer 1873–4) contained subgeneric names but did not list species.
CD’s copy of Pfeiffer 1873–4 was given to the the library of the Linnean Society. A slip pasted in the first volume reads, ‘For the Linnean Soc. presented by Ch. Darwin | Down. Oct. 26 1875’.


Describes observations by his son Horace on the extreme sensitivity of twisted seeds to moisture.

Letter details

Letter no.
Charles Robert Darwin
Joseph Dalton Hooker
Sent from
Source of text
DAR 95: 397–8
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 10209,” accessed on 24 May 2017,

Also published in The Correspondence of Charles Darwin, vol. 23