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Darwin Correspondence Project

To Francis Darwin   23 October [1873]

Oct 23rd

See P.S

My dear F.

If in the collection there are specimens of Desmodium gyrans from different districts, observe whether the little lateral leaflets differ in size on full-grown leaves.1 Look out for any abnormal projection at apex of leaflet, though excessively improbable— or for the abortion of the blade alone.—

In my living specimens—some of the leaves have 2 leaflets, some one & some none. The 2 little leaflets either stand exactly opposite each other or not so. How are these points with plants in a state of nature?

I have a wild hypothesis that the little leaflets may be tendrils reconverted into leaflets, as I believe to be the case with the grass-like leaves of Lathyrus nissolia & almost certainly with the little stipule-like projection at the end of the leaf of the common Bean.—Vicia faba.2

Your affect | C. Darwin

P.S. | Thank Sanderson cordially for his most kind assistance.— The Hæmoglobin was at first very dark red-brown; I shd be very glad to know whether it is meta-hæmoglobin.—3


CD had asked Francis to look at specimens of Desmodium at the Royal Botanic Gardens, Kew (see letter to Francis Darwin, 22 October 1873). Desmodium gyrans is now Codariocalyx motorius, the telegraph or semaphore plant.
Lathyrus nissolia is the grass vetchling; Vicia faba is the broad or fava bean. Both are in the family Fabaceae. CD believed that L. nissolia had developed from a twining plant with leaves to a leaf climber, with the leaves gradually developing into tendrils, which later lost their revolving and prehensile power and turned back into grass-like leaves (see Climbing plants, pp. 114–15).
CD may have asked John Scott Burdon Sanderson to analyse the ‘dark red granules, prepared from bullock’s blood’ described in Insectivorous plants, p. 121; Burdon Sanderson thought they were probably haematin, a component of metahaemoglobin. CD was testing the effect of various substances on the insectivorous plant Drosera rotundifolia (common or round-leaved sundew).


Wants FD to look at the little lateral leaflets of Desmodium. CD has "a wild hypothesis that the little leaflets may be tendrils reconverted into leaflets".

Letter details

Letter no.
Charles Robert Darwin
Francis Darwin
Sent from
Source of text
DAR 271.3: 11
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9110,” accessed on 23 March 2018,

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