From T. H. Farrer 8 August 1869
Abinger Hall, | Dorking.
8 August /69
My dear Mr Darwin
You remember mentioning the separate stamen of papilionaceous flowers as a point worth looking into.1 I have had too much to do to pay proper attention to it, but cannot help thinking that its function is to give the insects proboscis access to the nectar. In many cases where it does not exist. eg. Sarothamnus—Ulex—Genista Ononis—Lupin—the staminal tube is a tight fitting, thin tough, jacket to the pistil, with no space for nectar at foot between it and the pistil, & no space for a proboscis. In some at any rate of these flowers—the bees, which visit them constantly, certainly dont get what they want from the inside, but from the outside of the staminal tube. On the other hand in Lathyrus Pisum, Phaseolus, Robinia, Faba, where the 10th stamen is quite or partly separate, it is stiff & expands at bottom so as to leave between it & the pistil a cavity, in which there is nectar. And where the stamen is not quite separate all the way, it is separated at the bottom so as to leave a passage into the nectary.2
There are many other interesting points in these flowers illustrating your views about fertilization—eg the position of the flower before at and after blossoming— Invariably, as far as I have seen, the flower when in bloom is so placed as to make the wings & keel (or in one or two cases; the vexillum), a tempting lighting place for insects.— Almost, though not quite, as invariably, the bud and the pod are in quite different positions.— What can be more curious than to see the Common Pea3—the bud pendent: with the peduncle bent—straightening & lifting itself with the blossom—and again drooping in the pod? or again, the Lupin with a precisely opposite motion?
Except perhaps the still more curious case of the pendent racemes of Laburnum or Robinia, where the peduncle of each flower takes a half twist as it approaches blossoming, so as to bring the wings and keel into the same position as they usually occupy on an upright spike.
Again the brush on the style of Lathyrus: Vicia & Faba in its different positions, obviously serves to sweep out the pollen from the different shaped keels.
But I shall get tedious—and hope to be able when once well settled here to follow this up.
Hooker has promised to come and see us in our new abode in the course of the autumn, when I return from an official cruise amongst Lighthouses4 and Lockyer has promised to come & set me up a Telescope—5 I fear there is no chance of getting you to come and meet them: it would not be till the latter end of September or beginning of October.
We had a visit from the Leith Hill place party yesterday—but I have not yet been here long enough to go & see & envy their lovely view.6
Believe me | Very truly yours | T H Farrer
Charles Darwin Esqr FRS
Speculates on the function of the separate stamen of papilionaceous flowers.
Please cite as
Darwin Correspondence Project, “Letter no. 6857,” accessed on 20 January 2017, http://www.darwinproject.ac.uk/DCP-LETT-6857