To James Drummond 16 May 1860
Down, Bromley, Kent
May 16th. 1860.
I hope that you will excuse the liberty which I take in writing to you and asking you a favour.—1 Dr. Hooker has told me that I may use his name as an introduction.— I am very curious about the fertilisation of Leschenaultia formosa. I must just allude to its structure, though no doubt you are well acquainted with it. The indusium or cup at the summit of the pistil is open in the bud, but before the flower opens the indusium closes and in closing includes nearly all the pollen.— In my greenhouse the indusium never opens again. The pollen within the indusium is enclosed near the lips, and not a grain lies, as I find, on the stigmatic surface at the bottom of the indusium. How then is the plant fertilised?2
My belief is that insects in creeping in to suck the copious nectar brush open the indusium, and the hairs of their abdomens stir up the pollen and push it down on to the stigmatic surface. I find that this easily effected by a camel-hair brush. Now what I want to beg is for you to have the great kindness to watch for a short time the Leschenaultia and see whether Bees visit it; and if they do, to endeavour to observe whether in crawling in or whilst sucking, they do not open the lips of the indusium. As this plant may be visited by nocturnal insects, it would be a very interesting experiment to cover over with bag on frame made of very open gauze one or two plants (plucking off any open flowers) and then see whether they seed at all or less freely than plants left to the visits of insects.—3
This may appear a trifling enquiry to you; but the subject has been largely discussed by R. Brown, Aug: St. Hilaire4 and other celebrated Botanists; and Dr. Hooker and I are experimenting on the subject.— If any other Goodenaceæ, furnished with an indusium, grow near you, I should be infinitely obliged for any notices on their structure in relation to the following point, “how in one flower is it possible that pollen from another flower or plant of the same species could get into the indusium,” I have strong reason to believe that this is a universal possibility. In the Leschenaultia, if insects open the indusium in the manner in which I suspect, their abdomens dusted with pollen from one flower might easily carry grains into the indusium of another flower.
I hope that you will excuse the liberty I take in begging this favour and | I remain, Dear Sir | Your obliged Servant | Charles Darwin
Asks JD to observe Leschenaultia formosa to verify CD’s hypothesis of how it is fertilised. Also suggests an experiment to determine whether it is fertilised by nocturnal insects.
Please cite as
Darwin Correspondence Project, “Letter no. 2803,” accessed on 30 August 2016, http://www.darwinproject.ac.uk/DCP-LETT-2803