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 uncommon!}' 

 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 



