Climbing Plants 239 



wise explains how it is that plants twine." The 

 hop and the honeysuckle always move in the 

 same direction as the hands of a watch (Fig. 66). 

 They follow the sun. The bean, jasmine, wis- 

 taria, and convolvulus turn always in the contrary 

 direction to the hands of a watch, or against 

 the sun. A few vines notably the bittersweet 

 seem indifferent which way they twine, and one 

 species studied by Darwin, the Scypanthus elegans^ 

 can revolve first one way and then the other; 

 can, in fact, " reverse" like an expert waltzer. 



But the great majority of those which have 

 been studied twine always the same way, and as 

 a rule plants near of kin wind about their sup- 

 ports in the same direction. The speed of the re- 

 volving movement varys greatly. The convolvulus 

 and the bean sweep completely around the circle 

 in less than two hours. On the other hand, 

 some plants take twenty-four hours for a single 

 revolution, and one sluggard was found which 

 seemed unable to get around in less than forty- 

 eight hours. The rate of speed seems to have 

 little to do with the thickness of the vine, for 

 the woody shoots of the wistaria are found to 

 traverse the circle faster than do the slender 

 herbaceous tips of the morning-glories. 



