Believes species have arisen, like domestic varieties, with much extinction, and that there are no such things as independently created species. Explains why he believes species of the same genus generally have a common or continuous area; they are actual lineal descendants.
Discusses fertilisation in the bud and the insect pollination of papilionaceous flowers. His theory explains why, despite the risk of injury, cross-fertilisation is usual in the animal and vegetable kingdoms, even in hermaphrodites.
Down Bromley Kent
My dear D
What you say about extinction, in regard to small genera & local
disjunction, being hypothetical seems very just. Something
direct, however, could be advanced on this head from fossil shells; but hypothetical
such notions must remain. It is not a little egotistical, but I
I must say one word more in justification (for I feel sure that your tendency will be to despise me & my crotchets) that all my notion about how species change are derived from long-continued study of the works of (& converse with) agriculturists & horticulturists; & I believe I see my way pretty clearly on the means used by nature to change her species & adapt them to the wondrous & exquisitely beautiful contingencies to which every living being is exposed.
Thank you much for what you say about possibility of crossing of the grasses: I have been often astounded at what Botanists say on fertilisation in the bud: I have seen Cruciferæ mentioned as instance, which every gardener knows how difficult it is to protect from crossing!
What you say on Papilionaceous flowers is very true; & I have no facts to show that varieties are crossed; but yet (& the same remark is applicable in a beautiful way to Fumaria & Diclytra as I noticed many years ago) I must believe that the flowers are constructed partly in direct relation to the visits of insects; & how insects can avoid bringing pollen from other individuals I cannot understand. It is really pretty to watch the action of a Humble -Bee on the scarlet Kidney Bean, & in this genus (& in Lathyrus grandifloris) the honey is so placed that the Bee invariably alight on that one side of the flower towards which the spiral pistil is protruded (bringing out with it pollen) & by the depression of the wing-petal is forced against the Bee's side all dusted with pollen. N.B if you will look at bed of scarlet Kidney Bean you will find that the wing-petals on the left-side alone are all scratched by the tarsi of the Bees. In the Broom the pistil is rubbed on centre of back of Bee &c. &c.— I suspect there is something to be made out about the Leguminosæ which will bring the case within our theory; though I have failed to do so.
Our theory will explain why in vegetable & animal kingdom the act of fertilisation even in hermaphrodites usually takes place sub-jove, though thus exposed to the great injury from damp & rain. In animals in which the semen cannot, like pollen, be occasionally carried by insects or wind; there is no case of land-animals being hermaphrodite without the concourse of two individuals.
But my letter has been horribly egotistical: but your letters always so greatly interest me; & what is more they have in simple truth been of the utmost value to me.
Your's most sincerely & gratefully | C. Darwin
- f1 2125.f1Dated on the basis of a note about kidney beans (see n. 6, below), the substance of which is repeated in the letter.
- f2 2125.f2See letter from Asa Gray, 7 July 1857.
- f3 2125.f3CD had asked Joseph Dalton Hooker to read and comment on the draft of his chapter on geographical distribution (see letters to J. D. Hooker, 30 July  and [16 October 1856]).
- f4 2125.f4See letter from J. D. Hooker, 9 November 1856.
- f5 2125.f5CD alluded to the cross-pollination of Fumaria by insects in his species book (Natural selection, p. 53).
- f6 2125.f6This sentence was added in the margin. In DAR 49: 47, there is a note dated ‘July 19/57’ that reads: ‘The left-wing-petal flower *(to you [interl] facing *it [above del’you‘]) of Kidney Bean are all scratched & disfigured by the tarsi of the Bees.—’.
- f7 2125.f7That is, the theory that all organic beings must occasionally cross-fertilise.
- f8 2125.f8Literally, under Jupiter (the sky-god), that is, in the open air. CD maintained that although fertilisation in the bud did occur, it was never normal and regular (see letter to Asa Gray, 18 June ).