To Fritz Müller 31 July 1
Down. | Bromley. | Kent. S.E.
My dear Sir
I received a week ago your letter of June 2. full as usual of valuable matter & specimens.2 It arrived at exactly the right time, for I had just completed, & was enabled to correct a pretty full abstract of your observations on the plant’s own pollen being poisonous. I have inserted this abstract in the proof sheets in my chapter on sterility, & it forms the most striking part of my whole chapter.3 I thank you very sincerely for these most interesting observations, which however I regret that you did not publish independently. I have been forced to abbreviate one or two parts more than I wished—viz. about the fertility of the Epidendreae & on the advantage to the plant of the pollen being poisonous, for I was not quite sure that I understood parts of your letter.4 The seeds which you have sent are very valuable.5 Your letters always surprize me from the number of points to which you attend. I wish I cd make my letters of any interest to you, for I hardly ever see a naturalist & live as retired a life as you in Brazil. The terrestrial Orchis with the pollen-staff seems very curious; my first impression was that it was allied to Spiranthes. With respect to mimetic plants I remember Hooker many years ago saying he believed that there were many, but I agree with you that it wd be most difficult to distinguish between mimetic resemblance & the effects of peculiar conditions.6 Who can say to which of these causes to attribute the several plants with heath-Erica-like foliage at the C. of Good Hope?7 Is it not also a difficulty that quadrupeds appear to recognize plants more by their odour than their appearance? What I have just said reminds me to ask you a question: Sir J. Lubbock brought me the other day what appears to be a terrestrial planaria (the first ever found in the northern hemisphere) & which was coloured exactly like our dark coloured slugs. Now slugs are not devoured by birds like the shell-bearing species, & this made me remember that I found the Brazilian planariæ actually together with striped Vaginuli which I believe were similarly coloured.8 Can you throw any light on this? I wish to know, because I was puzzled some months ago how it wd be possible to account for the bright colours of the planariæ in reference to sexual selection. By the way I suppose they are Hermaphrodites?9
Do not forget to aid me, if in yr power, with answers to any of my questions on expression, for the subject interests me greatly.10
with cordial thanks for yr never failing kindness | believe me yours very sincerely | Charles Darwin
Has abstracted for insertion in his sterility chapter [Variation 2, ch. 18], FM’s observations of plant’s pollen being poisonous to itself.
Occurrence of mimetic plants.
Colouring of Planariae.
Please cite as
Darwin Correspondence Project, “Letter no. 5591,” accessed on 23 October 2016, http://www.darwinproject.ac.uk/DCP-LETT-5591