312 CLIMBING AND [1863. 



branch (i.e. the stem between the two uppermost leaves ex- 

 cluding the growing tip) is constantly and slowly twisting round 

 making a circle in from one and a half to two hours ; it will 

 sometimes go round two or three times, and then at the same 

 rate untwists and twists in opposite directions. It generally 

 rests half an hour before it retrogrades. The stem does not 

 become permanently twisted. The stem beneath the twisting 

 portion does not move in the least, though not tied. The move- 

 ment goes on all day and all early night. It has no relation to 

 light, for the plant stands in my window and twists from the 

 light just as quickly as towards it. This may be a common 

 phenomenon for what I know, but it confounded me quite, 

 when I began to observe the irritability of the tendrils. I do 

 not say it is the final cause, but the result is pretty, for the plant 

 every one and a half or two hours sweeps a circle (according 

 to the length of the bending shoot and the length of the 

 tendril) of from one foot to twenty inches in diameter, and 

 immediately that the tendril touches any object its sensitive- 

 ness causes it immediately to seize it ; a clever gardener, my 

 neighbour, who saw the plant on my table last night, said : 

 " I believe, Sir, the tendrils can see, for wherever I put a 

 plant it finds out any stick near enough." I believe the 

 above is the explanation, viz. that it sweeps slowly round and 

 round. The tendrils have some sense, for they do not grasp 

 each other when young. 



Yours affectionately, 



C. DARWIN. 



C. Darwin to J. D. Hooker. 



Down, July 14 [1863], 



MY DEAR HOOKER, I am getting very much amused by 

 my tendrils, it is just the sort of niggling work which suits 

 me, and takes up no time and rather rests me whilst writing. 

 So will you just think whether you know any plant, which 



