To J. D. Hooker 14 July 
My dear Hooker
I am getting very much amused by my tendrils— it is just the sort of niggling work which suits me & takes up no time & rather rests me whilst writing.1 So will you just think whether you know any plant, which you could give or lend me or I could buy with tendrils remarkable in any way, for development, for odd or peculiar structure or even for odd place in natural arrangement.—2 I have seen or can see Cucurbitaceæ—Passion-flowers—Virginian creeper—Cissus discolor—common Pea & Everlasting pea.—3 It is really curious the diversification of irritability (I do not mean the spontaneous movement, about which I wrote before & correctly as further observation shows);4 for instance I find a slight pinch between thumb & finger at end of tendril of Cucurbitaceæ causes prompt movement, but a pinch excites no movement in Cissus.— The cause is that one side alone, (the concave) is irritable in former; wheres both sides are irritable in Cissus, so if you excite at same time both opposite sides there is no movement; but by touching with a pencil the two branches of tendril in any part whatever you cause movement towards that point; so that I can mould by mere touch the two branches into any shape I like
&c &c The peduncle of tendril is either not sensitive or sensitive only to prolonged though slight pressure &c &c.—5
If you can screw out a little time do come here for a Sunday, I shd. so like it, & I have been better of late & shd. stand some talking well.—
What a splendid number the last of N. Hist. Review.—6 Capital, as they seemed to me, Botanical & Zoological papers.— The embryology of Echinodermata seemed capitally done.7 I suppose I owe to Oliver the capital & clear article on Linum.8
GoodBye, it is awfully hot.— Ever yours affect— | C. Darwin
Requests tendril-bearing plants.