CLIMBING PLANTS. 125 



revolving shoot was 31 inches long. " The extreme 

 tip thus made a circle of above 5 feet (or 62 inches) 

 in diameter and 16 feet in circumference, travel- 

 ling at the rate of 32 or 33 inches per hour. The 

 weather being hot, the plant was allowed to stand 

 on my study-table ; and it was an interesting spec- 

 tacle to watch the long shoot sweeping this grand 

 circle, night and day, in search of some object 

 round which to twine." 1 



Most twiners move around in the contrary direc- 

 tion from the hands of a watch, but a few move 

 from the left to the right of the observer. In rare 

 cases the direction may reverse in the same plant. 

 This reversal happens frequently with leaf-climbers. 

 Tropceolum (Garden Nasturtium) is a good example 

 of this class of plants, where the petioles of the 

 leaves clasp the support (Fig. 35). The young 

 shoots of leaf-climbers revolve like the stems of 

 twiners, and in some cases the leaves revolve also. 

 " The object gained by the revolving movement is 

 to bring the petioles, or the tips of the leaves, into 

 contact with surrounding objects ; and without this 

 aid the plant would be much less successful in 

 climbing. With rare exceptions, the petioles are 

 sensitive to contact only whilst young. . . . They 



. i " Climbing Plants," p. 6. 



