Chap. II. CLEMATIS. 59 



slowly increased until the petiole moved through, nearly 

 ninety degrees : beyond this it did not move ; nor did 

 the petiole, the loop remaining suspended, ever become 

 perfectly straight again. 



When we consider, on the one hand, the thickness 

 and stiffness of the petioles, and, on the other hand, 

 the thinness and softness of fine cotton thread, and 

 what an extremely small weight one-sixteenth of a 

 grain (4*05 mg.) is, these facts are remarkable. But 

 I have reason to believe that even a less weight excites 

 curvature when pressing over a broader surface than 

 that acted on by a thread. Having noticed that 

 the end of a suspended string which accidentally 

 touched a petiole, caused it to bend, I took two 

 pieces of thin twine, 10 inches in length (weighing 

 l - 64 gr.), and, tying them to a stick, let them hang as 

 nearly perpendicularly downwards as their thinness 

 and flexuous form, after being stretched, would per- 

 mit; I then quietly placed their ends so as just 

 to rest on two petioles, and these certainly became 

 curved in 36 hrs. One of the ends touched the anode 

 between a terminal and lateral sub-petiole, and it was 

 in 48 hours caught between them as by a forceps. In 

 these cases the pressure, though spread over a wider 

 surface than that touched by the cotton thread, must 

 have been excessively slight. 



Clematis vitalba. The plants were in pots and not 

 healthy, so that I dare not trust my observations, which 

 indicate much similarity in habits with C.flammula. I 

 mention this species only because I have seen man\ 



