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Darwin Correspondence Project

From T. H. Farrer   [before 10 April 1874]1

Abinger Hall, | Wotton. Surrey (Post Town) | Gomshall (Station) S.E.R.

My dear Mr Darwin

Hurrah for Coronilla! C. montana—a smaller & more delicate plant than our old C. varia has no possible nectar inside the flower—but the calyx is covered with minute cells full of liquid— Many aphides on them.2

C. Emerus (lutescens)3 has the same general structure as the others: but elongated— The calyx has no moisture on the outside but the staminal tube ends at the base in a regular nectar cavity with apertures on each side like a pea: the cavity full of nectar. C. Emerus—the common form will be in full blossom soon & I hope to see bees at it.

In C. Emerus lutescens there is a curious projection on the inside of the claw of the vexillum.4 I suspect it tells the bee that it must put its nose—quite out of its sight—to the right or left in order to get to the nectar holes. But if this is all true I dont know why the bee should not go in by the back door. Nous verrons.5

At any rate here is a case where in the same genus all have a free tenth stamen— some have as usual in that case nectar in the staminal tube— others have not the nectar there—but have it outside the calyx with a peculiar arrangement of the petals enabling the bee to get at it there.

This helps to explain the free 10th stamen; serviceable in some, rudimentary in others.

Your son should look at the projection on the claw of C. Emerus lutescens.6

Poor Effie7—so seldom laid up has been in misery with a bad tooth and is gone up with Hope8 to get rid of it. This damps our owise pleasant Easter in the new house

Yrs most truly | T H Farrer

Which came first—free 10th stamen or peculiar aperture at base of petals?


The date is established by the relationship between this letter and the letter to T. H. Farrer, 10 April 1874.
Farrer had been examining the morphology of Coronilla, a genus of crown vetch. In many papilionaceous flowers, nine stamens fuse to form a tube-like structure, with the tenth remaining free, leaving the tube unclosed and allowing an insect access to the nectar (see Correspondence vol. 21, letter to T. H. Farrer, 10 August [1873] and n. 2). Farrer had observed flowers of C. varia that lacked the usual nectar at the base of the free staminal tube, but that appeared to have nectar-filled cells on the surface of the calyx (see Correspondence vol. 21, second letter from T. H. Farrer, 12 August [1873], and letter to T. H. Farrer, 14 August 1873). Coronilla montana is now C. coronata; C. varia is now Securigera varia.
Coronilla emerus is now Hippocrepis emerus.
The vexillum is the large upper petal in papilionaceous flowers.
Nous verrons (French): we will see.
Farrer refers to Francis Darwin. In Farrer 1874, p. 170, he wrote: ‘In C. emerus lutescens … there is a curious little excrescence on the inside of the claw of the vexillum just above the calyx. Does it guide the bee’s proboscis to the apertures in the staminal tube, which it is to be remembered are on each side of the central tenth stamen? Mr. F. Darwin has suggested a function of this kind for a somewhat similar structure on the free tenth stamen of Phaseolus.’
Katherine Euphemia Farrer was Farrer’s wife.
Hope Elizabeth Wedgwood was Effie Farrer’s sister.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Farrer, Thomas Henry. 1874. Fertilisation of papilionaceous flowers—Coronilla. Nature, 2 July 1874, pp. 169–70.


Observations on Coronilla.

Letter details

Letter no.
Thomas Henry Farrer, 1st Baron Farrer
Charles Robert Darwin
Sent from
Abinger Hall
Source of text
DAR 164: 77
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 8854,” accessed on 26 October 2021,

Also published in The Correspondence of Charles Darwin, vol. 22