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Darwin Correspondence Project

From Francis Darwin   [16 or 17 August 1873]1

Pantlludw | Machynlleth

Dear Father

I find our pea is L. sylvestris not maritimus; I very stupidly took it for granted it must be maritimus, as it grew on the cliff, luckily I thought I would look & make sure.2 Isnt it odd the bees should bite there and not the garden ones, wh Bentham says is only a broad leaved variety—3 I think I have made out why they split to the right of the loose stamen but I’m not certain yet.

[DIAG HERE]

In very young buds the brush of the style points directly backwards as in this figure so that it would not brush the bee, but in old peas it is twisted so that the direction of the hairs is perpr to paper in my figure; and as the bee goes in it always comes up on his right side & brushes him.4 In the vetch where the tuft of hair is just the reverse, there is no twisting as it would easily brush the bee without and here the pod in growing does not split up the tube to the right of the loose stamen but lifts it up like a lid as it grows, show’g that it is the twisting that makes the tube in peas split to the right of the stamen— We will make it out—& I will explain better—

I have no time as I must be off | Yrs affec | FD

Footnotes

The date is established by the relationship between this letter and the letters to Francis Darwin, 15 August [1873] and 18 [August 1873].
See letter from Francis Darwin, 14 August [1873] and n. 2. The reference is to Lathyrus sylvestris and L. maritimus.
In his Handbook of the British flora (Bentham 1865, 1: 231), George Bentham had included under the heading ‘Everlasting pea. Lathyrus sylvestris, Linn.’ a brief description of ‘a broad-leaved variety from southern Europe’, which he noted, ‘has been distinguished as a species, under the name L. latifolius’.
The stylar brush is a mechanism that promotes crossing in many papilionaceous flowers. In such flowers, the anthers dehisce (open up) before the flower opens and the stigma becomes receptive, depositing pollen on the hairs (brush) of the style, thus ensuring that a bee approaching the flower would first contact the stigma and deposit pollen before coming into contact with the pollen on the stylar brush. The asymmetry of the keel in Lathyrus sylvestris and L. latifolius causes a bulge in the tip of the keel on the left side only, which guides the style when a bee depresses the keel on that side. Twisting of the style begins in the bud stage and the final divergence is about 90o. For more on the function of the stylar brush in Lathyrus, see Westerkamp 1992, pp. 124–6.

Summary

Gives his opinion on why tubes of peas split to the right of the loose stamens [inLathyrus sylvestris].

Letter details

Letter no.
DCP-LETT-9012
From
Francis Darwin
To
Charles Robert Darwin
Sent from
Machynlleth
Source of text
DAR 77: 140–1
Physical description
3pp

Please cite as

Darwin Correspondence Project, “Letter no. 9012,” accessed on 16 December 2017, http://www.darwinproject.ac.uk/DCP-LETT-9012

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

letter