Chap. IV. PASSIFLORACE^. 155 



not agitated by the wind. The movement after a touch 

 is very rapid : I took hold of the lower part of several 

 tendrils, and then touched their concave tips with a 

 thin twig and watched them carefully through a lens ; 

 the tips evidently began to bend after the following 

 intervals— 31, 25, 32, 31, 28, 39, 31, and 30 seconds ; so 

 that the movement was generally perceptible in half a 

 minute after a touch ; but on one occasion it was 

 distinctly visible in 25 seconds. One of the tendrils 

 which thus became bent in 31 seconds, had been 

 touched two hours previously and had coiled into a 

 helix; so that in this interval it had straightened 

 itseK and had perfectly recovered its irritability. 



To ascertain how often the same tendril would 

 become curved when touched, I kept a plant in my 

 study, which from being cooler than the hot-house was 

 not very favourable for the experiment. The extremity 

 was gently rubbed four or five times with a thin stick, 

 and this was done as often as it was observed to have 

 become nearly straight again after having been in 

 action ; and in the course of 54 hrs. it answered to the 

 stimulus 21 times, becoming each time hooked or 

 spiral. On the last occasion, however, the movement 

 was very slight, and soon afterwards permanent spiral 

 contraction commenced. No trials were made during 

 the night, so that the tendril would perhaps have 

 answered a greater number of times to the stimulus ; 

 though, on the other hand, from having no rest it 

 might have become exhausted from so many quickly 

 repeated efforts. 



