To J. D. Hooker 21 October 1
Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.
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 price.8 It is folly for me to keep such a book.
Ever yours affecty | C. Darwin
Describes observations by his son Horace on the extreme sensitivity of twisted seeds to moisture.
Please cite as
Darwin Correspondence Project, “Letter no. 10209,” accessed on 22 October 2016, http://www.darwinproject.ac.uk/DCP-LETT-10209