To T. H. Farrer   14 August 1873

Bassett Southampton

Aug 14. 1873

My dear Farrer

You are the man to conquer a Coronilla. I have been looking at the half-dried flowers, & am prepared to swear that you have solved the mystery.1 The difference in the size of the cells on the calyx under the vexillum right down to the common peduncle2 is conspicuous. The flour still adhered to this side. I see little bracteæ or stipules apparently with glandular ends at the base of the calyces. Do these secrete? It seems to me a beautiful case.

When I saw the odd shape of the base of the vexillum I concluded that it must have some meaning, but little dreamt what that was. Now there remains only the one serious point, viz. the separation of the one stamen. I dare say that you are right in that nectar was originally secreted within the staminal tube; but why has not the one stamen long since cohered? The great differences in structure for fertilization within the same genus makes one believe that all such points are very variable. With respect to the non-coherence of the one stamen, do examine some flower-buds at a very early age; for parts which are largely developed are often developed to an unusual degree at a very early age; & it seems to me quite possible that the base of the vexillum (to which the single stamen adheres) might thus be developed & thus keep it separate for a time from the other stamens. The cohering stamens to the right & left of the single one seem to me to be pushed out a little laterally. When you have finished yr observations, you really ought to send an account with a diagram to Nature, recalling yr generalization about the diadelphous structure, & now explaining the exception of coronilla.3

Do add a remark how almost every detail of structure has a meaning when a flower is well examined.4

Your observations pleased me so much that I cd not sit still for $\frac{1}{2}$ an hour, & if Effie5 had been here she wd. have had a good laugh at me—

Please to thank Mr Payne for his remarks, which are of value to me with reference to Mimosa.6 I am very much in doubt whether opening the sashes can act by favouring the evaporation of the drops: may not the movement of the leaves shake off the drops or change their places? If Mr Payne remembers any plant which is easily injured by drops I wish he wd put a drop or two on a leaf on a bright day, & cover the plant with a clean bell glass, & do the same for another plant, but without a bell glass over it, & observe the effects.

Thank you much for wishing to see us again at Abinger7 & it is very doubtful whether it will be Coronilla, Mr Payne, the new garden, the children, Effie, or yourself which will give me the most pleasure to see again—

yours most sincerely | Ch. Darwin

It will be curious to note in how many years the rough ground becomes quite uniform in its flora

P.S. One may feel sure that primordially nectar was secreted within the flower & then excreted by the calyx, as in some species of Iris & Orchids. This latter being taken advantage of in Coronilla, would allow of the secretion within the flower ceasing, & as this change was going on in the two secretions, all the parts of the flower would become modified & correlated.—

Footnotes

See letter from T. H. Farrer, 12 August [1873]. Farrer was investigating the floral morphology of Coronilla with a view to discovering the source of nectar and the methods used by insects to collect it. Many of the species formerly included in the genus Coronilla have now been reclassified; for currently accepted species, see Lassen 1989, pp. 59–60.
The common peduncle is the stem supporting the whole inflorescence; the pedicels of the individual flowers unite at the top of it.
Farrer’s observations were published in Nature (Farrer 1874). The generalisation CD mentioned was that monadelphous species (those where the tenth stamen is fused) lacked nectar in the staminal tube, in contrast to diadelphous species, which had nectar in the staminal tube. Coronilla was considered to be diadelphous but lacked intrastaminal nectar (see Farrer 1874, p. 169).
In Farrer 1874, p. 169, Farrer included a general paragraph referring to the correlation of function and structure in different floral parts.
Katherine Euphemia Farrer.
George Payne’s observations on water damage in leaves were communicated to CD by Farrer in his letters of 12 August 1873 and 12 August [1873]. Mimosa is the genus of sensitive plants.
CD visited Abinger from 5 to 9 August 1873 (see ‘Journal’ (Appendix II)).

Summary

Thinks THF has solved the mystery of Coronilla.

Letter details

Letter no.
DCP-LETT-9010
From
Charles Robert Darwin
To
Thomas Henry Farrer (1st Baron Farrer)
Sent from
Bassett
Source of text
Linnean Society of London (Farrer 21)
Physical description
8pp