My dear Hooker

I was surprised & pleased to get your last note; for I did not at all expect another.—² We were amused at your original views on insanity.—   My Father thought something the same; at least he thought almost everyone was insane on some point. Thank you much for thinking about Asses & Mules: the forked stripe on shoulder is a very curious point (& I have seen traces of it) for the meaning of the fork is plain when the legs are transversely barred, but is an absurdity (except on doctrine of inheritance) with an animal with unstriped legs.—³ If you go up lofty mountains compare general state of vigour of the first individuals of any species of plant, which you meet, with the last, with respect to struggle for life, as alluded to in Origin—;⁴ also the degree of abruptness of limitation of the species.—

The rest of this letter I write to amuse myself & not for your sake, as I have a weakness, that I can never enjoy my work, till I have told you.— You are my public.—   But before I begin, I must say how entirely agree about the detestable article in Athenæum about Tyndall—sneering at his veracity—& very disagreeable about Huxley.—⁵ I look at the Editor as a spiteful old woman, who has taken, what my Brother calls her D.B. degree (ie damned bitch)—⁶

With respect to Drosera, there is no doubt that the plant is acute enough & knows what is good. It releases from its gripe an inorganic body far sooner than an organic body. But fluids show the difference better than the act of mere releasing. I have tried only the following 14 fluids, made as nearly as possible the same thin consistency, & in most case each fluid on several leaves. Water, syrup of sugar, starch, gum, olive-oil—sherry wine, carbonate of soda; these contain no nitrogen & never cause any inflection of the leaves or hairs. On other hand, milk cold infusion of raw meat, urine, raw white of egg, thin gelatine, thin mucus from lungs, & saliva all cause most powerful contraction & all contain nitrogen.—   Saliva contains less than one percent of animal matter. But here comes the really curious case, a solution in proportion of 1 grain of Carbonate of Ammonia to 1 oz of water (ie 1 to 480 parts by weight) & of this solution $\frac{1}{2}$ minim being taken, positively & certainly produces great effect. Hence $\frac{1}{960}$ of one grain of C. of Ammonia causes contraction. This evening I rerepeated experiment on 5 leaves (on some of which I had put drop of distilled water in morning with no effect) & all are now contracted. Is this not curious? Nor am I got to minimum strength of solution yet.—⁷

I daresay you had no time to read my note of action of rostellum in Malaxis & Epipactis.⁸ I have now examined Spiranthes autumnalis (for God’s sake if you find any odd genus of Orchis if you can, put it in weak spirits with buds & old flowers for me, for I am fairly mad on subject) & in Spiranthes we have new & curious modification, which I must publish to you my public.⁹ Within the rostellum, there is formed a hard canoe-shaped object; placed vertically, ie parallel to axis of flower; the anthers shrivel & leave pollinia lying at back of rostellum (as in Listera) in bud, & the rostellum splits behind, & the pollinia become permanently attached to the now naked bottom of “canoe”. Now the flower opens. If you then touch most delicately the rostellum in front (ie on side over the stigmatic surface,) the external membrane by a vital action instantly splits longitudinally down its whole length, & exposes the open part of canoe, which canoe is filled with extremely viscid matter; & this viscid matter sets instantly hard (as in Listera), so that the touching object—(a bristle or probosis of insect) is glued firmly to the “canoe” & this being already glued to the pollinia, all are withdrawn together. The rostellum then presents a split appearance. The membranous edges of the now split rostellum form the two foliaceous projections to the rostellum described by some authors!¹⁰ If you can understand this, you will think it is cerious modification of the Listera type of structure.

Farewell my dear Hooker. Do take care of yourself.—   I am very glad your family approve of your Expedition.¹¹ It is wonderfully spirited.

Farewell    may you prosper | Yours affectionately | C. Darwin

I have written all this for my enjoyment & not a bit for yours.—