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Darwin Correspondence Project

From Francis Darwin   [25 August 1873]1



Dear Father


Many thanks for your second letter— I am sorry our brush theory is wrong; anyhow in the garden Sylvestris it does brush the bee and smear him with pollen.2 We are in a muddle about right and left. In future I shall use your notation, ie considering one self to be a bee going in & sitting on the keel; With this notation the brush in Garden Sylvestris was turned to the left in all we have looked at.3 With yr notation it is on the left that the bee bites the flower— He doesnt bite the keel at all, but, at the back of the vexillum between the left top and left lateral calyx teeth   If you take off the vexillum in Everlasting you will see that a hole is left between the calyx and the flange of the ala   In the wild one, I pushed a needle into one of the bitten hole, and then dissected the flower, and found it had gone straight into the nectar hole—4 But in the Garden Sylvestris the space left between the flange of the ala and the calyx is not so big and a needle does not go in of its own accord but a bee could undoubtedly get in by biting a hole, tho’ not so easily as it can in the wild one— They do not bite the stamen tube, and they must use the nectar holes as their bitten holes are directly over the nectar holes— It seems to me evident that the reason the bee goes to the left side (new notation) to bite his hole is that the pod splits up the left nectar hole and makes it bigger— In the garden everlasting the pod splits into the left in 15 out of 18 cases


In wild one 16 out of 22 (leaving out 2 doubtful ones).

Amy discovered L pratensis on Monday it has fine nectar holes.5 This Lathyrus confirms us in thinking it is the twisting of the stigma that makes the left nectar hole bigger by the pod splitting in that side— In L pratensis the stigma is not twisted—so we expected it would grow up in the middle lifting the loose stamen up like the lid of a box as V. cracca does, but the stamen is too tight on for this so it has to go on one side or the other of it; and we find that as there is no twist it comes up just as often on one side as the other— 3 buds of wild sylvestris had fertilized themselves— I will do the meat—6 We will cover up some everlastings— I dare say I have explained this all badly so dont try & understand it I can explain it when I come, and dont bother to answer—7 The nectar holes communicate at once I should think it would be just as easy for the bee to go to the left nectary from the right side of the flower—

Yrs affec | F Darwin

We have pouring weather generally

Dicky writes from Dartmoor, that when the sun appeared one day they cheered him— Mrs Ruck8 & Amy send their love—

CD annotations

Top of letter: ‘(Proof of skill in Bees, as they bite hole over the larger nectar-hole.)’ pencil


The date is established by the relationship between this letter and the letter to Francis Darwin, 18 [August 1873]. The Monday following 18 August 1873 was 25 August.
Francis had hypothesised that the location of the hairs on the stylar brush in different papilionaceous flowers was an adaptation related to the angle at which an insect approached the flower, but CD informed him that the location of the brush hairs was correlated with the form of the keel (see letter from Francis Darwin, [16 or 17 August 1873], and letter to Francis Darwin, 18 [August 1873]).
Francis refers to Lathyrus latifolius (the everlasting pea; see letter to Francis Darwin, 18 [August 1873] and n. 4).
In papilionaceous flowers, the vexillum or standard is the large central petal, and the alae or wing petals are the two exterior side petals that partially surround the carina or keel petals. The keel petals are united at the lower edge, forming a boat-like shape that hides the sexual parts of the flower. For more on the techniques used by different bees to get to nectar holes in Lathyrus latifolius, see Westerkamp 1993, pp. 129–34. Most Victorian authors identified the everlasting pea as Lathyrus sylvestris and categorised the garden everlasting pea as only a variety of the former. George Bentham had noted in his description that the garden variety had been distinguished as a species, under the name L. latifolius (Bentham 1865, 1: 231). Lathyrus latifolius is now considered to be a separate species.
Lathyrus pratensis is the meadow vetchling or meadow pea. Francis refers to Amy Ruck.
Francis may have intended to write ‘net’ here.
Emma Darwin’s diary (DAR 242) records Francis’s arrival from Wales on 2 September 1873.
Francis refers to Richard Matthews Ruck and Mary Anne Ruck.


Bentham, George. 1865b. Handbook of the British flora; a description of the flowering plants and ferns indigenous to, or naturalized in, the British Isles. For the use of beginners and amateurs. 2 vols. London: Lovell Reeve & Co.

Westerkamp, Christian. 1993. The co-operation between the asymmetric flower of Lathyrus latifolius (Fabaceae–Vicieae) and its visitors. Phyton: annales rei botanicae 33: 121–37.


Regrets that "our brush theory" is wrong.

Letter details

Letter no.
Francis Darwin
Charles Robert Darwin
Sent from
Source of text
DAR 77: 142–3
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 9016,” accessed on 21 October 2021,

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