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. 
