CLIMBING PLANTS. 119 



MY DEAR HOOKER, I have been observing pretty care- 

 fully a little fact which has surprised me ; and I want to 

 know from you and Oliver whether it seems new or odd 

 to you ; so just tell me whenever you write : it is a very 

 trifling fact, so do not answer on purpose. 



I have got a plant of Echlnocystis lobata [Fig. 33] to 

 observe the irritability of the tendrils described by Asa 

 Gray, and which, of course, is plain enough. Having the 

 plant in my study, I have been surprised to find that the 

 uppermost part of each branch (i.e., the stem between 

 the two uppermost leaves excluding the growing tip) is con- 

 stantly and slowly twisting round, making a circle in from 

 one-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. 1 The stem does not become perma- 

 nently 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, 



1 This reversal of the direction of the movement is not the normal 

 method of the plant. lie s js of it afterward ("Climbing Plants," 

 p. 128), " The course generally pursued was with the sun, but often in 

 an opposite direction. Sometimes the movement during a short time 

 would either stop or be reversed ; and this apparently was due to inter- 

 ference from the light, as, for instance, when I placed a plant close to 

 a window." 



