Darwin Letter Friday
Happy Independence Day! To celebrate, below is a letter written by Darwin on July 4, 1858 to an American: botanist Asa Gray. Gray pretty much started the botany program at Harvard, and was an immense help with developing Darwin’s carefully wrought theory.
Darwin observed peculiarities in Dicentra (Bleeding Heart) flowers that he links to the cross-pollinating effect of bees. Interesting stuff, to be sure, but there’s more. The final paragraph deals with the unexpected arrival of Wallace, and his presentation days ago (along with Wallace’s paper) to the Linnean Society. When Darwin wrote this letter, the theory of natural selection was coming together.
<< See Monday’s WIRED article about this presentation >>
Down Bromley Kent
July 4th.— 1858
My dear Gray
With respect to Dicentra it is really pretty to watch the Humble Bees sucking first on one or the other side of the several flowers; with their hind legs resting on the crests of the hood formed by the inner united petals they push it to opposite side of flower, & the straight pistil is rubbed against their abdomens & inner side of thighs, which are white with pollen from the several flowers. It is impossible but what the individuals of Dicentra must be largely crossed. Your Adlumia has not flowered with me yet. In Fumaria & Corydalis we have another structure, viz nectary on one side & here the pistil bends so that the 2 stigmas are presented in the gangway to the one nectary; & the hood slips off easiest in opposite direction, instead of equally easily to either side. [DIAGRAM HERE] Hood Dicentra nectary nectary Fumaria & Corydalis nectary Indeed, in Corydalis lutea it almost springs off, & the pistil decidedly springs towards the nectary-bearing petal. I have observed only 6 Fumariaceæ, & I wish that I knew whether the rule was general; for I must believe that the structure of these flowers is related directly to the visits of Bees.f3
I suspect from my own few observations that the following rule may be gen-eralised (& I shd. much like to know whether it is true) that when honey is secreted on one point of circle of corolla, the pistil if it bends, always bends so that the stigmas, when mature, lie in the gangway to nectary. Thus in Columbine where there is a circle of nectaries, the stigmas are straight; in Aquilegia grandiflora where there is one nectary, the stigmas are rectangularly bent so that every Bee (as I this day saw) brushes over them in extracting the honey.—
It is very unlikely, but if by any chance you have my little sketch of my notions of “natural Selection” & would see whether it or my letter bears any date, I shd. be very much obliged.f4 Why I ask this, is as follows. Mr. Wallace who is now exploring New Guinea, has sent me an abstract of the same theory, most curiously coincident even in expressions.f5 And he could never have heard a word of my views. He directed me to forward it to Lyell.— Lyell who is acquainted with my notions consulted with Hooker, (who read a dozen years ago a long sketch of mine written in 1844) urged me with much kindness not to let myself to be quite forestalled & to allow them to publish with Wallace’s paper an abstract of mine; & as the only very brief thing which I had written out was a copy of my letter to you, I sent it and, I believe, it has just been read, (though never written, & not fit for such purpose) before the Linnean Socy.;f6 & this is the reason, why I shd. be glad of the date. But do not hunt for it, as I am sure it was written in September, October or November of last year.—
I have troubled you with a long story on this head; so pray forgive me & believe me | Yours very sincerely | C. Darwin.—
P.S | In regard to bent pistils & nectaries, I shd. say that I largely judge of position of nectary, by seeing where Bees suck; according to this, the rule holds in all Leguminosæ, in my 6 Fumariaceæ, in Polygala.—Viola tricolor, Dictamnus Æsculus, Rhododendron—Aquilegia.