TWINERS AND CLIMBERS. 199 



such great favourites in recent times. Some of the 

 species of clematis retain the power of twining to a 

 limited extent, sometimes in the direction of the sun, 

 and with others in opposition to it. Not uncommonly 

 the same twig will twine two or three times in one 

 direction, then grow erect for a while, and afterwards 

 twine again in the opposite direction. They must 

 therefore be regarded as very inferior twiners. It 

 would be expected, a priori, that with this twining 

 power, the terminal joints also rotate, and this is the 

 fact. In one species the quickest revolution was made 

 in five hours and a half, in another in four hours and 

 twenty minutes, in another in three hours and three- 

 quarters, and in another in one hour and fifty 

 minutes. 



The petioles, or leafstalks, are so far sensitive to 

 the touch that after being rubbed, or otherwise irri- 

 tated, they bend towards the point of irritation, and 

 if a stick or twig presents itself in that direction, the 

 leafstalk bends round, and embraces it. If no ob- 

 ject is encountered by the bending petiole it soon 

 straightens itself again. The petioles are most 

 sensitive when young ; in some species the older 

 petioles lose their power of responding to irritation 

 altogether. In one instance a fragment of thin 

 cotton thread, weighing only one-sixteenth of a grain, 

 caused a petiole to bend perceptibly. 



" A thin stick placed so as to press lightly against 



