240 Field, Forest, and Wayside Flowers 



In all the leaf-climbers and tendril-bearers whose 

 habits have been investigated, the young internodes 

 revolve, but there movements are less regular than 

 those of the twiners. 



The tender shoots of that familiar leaf-climber, 

 the clematis, while growing vigorously in spring, 

 make small oval revolutions, moving always in the 

 same direction as the hands of a watch. Later 

 in the season the vine-tips travel more fitfully 

 and slowly through a very small circle, and by 

 midsummer their movements have almost ceased. 



But the leaf-stalks have acquired a high degree 

 of sensitiveness, as if to make up for the failing 

 powers of the shoots. 



While the leaf is yet so young that its blade 

 or flat, green surface has attained but one-sixth 

 of its full size, its stalk is so well developed that 

 the whole affair has somewhat the disproportioned 

 and lanky appearance of a few-days'-old colt. At 

 this stage of growth the sensitiveness of the leaf- 

 stalk is at its highest, and the tender blade is 

 bent downward, so that the whole leaf has a 

 hook-like form (Fig. 67). 



When the growth of the plant or an impulse 

 from the wind brings the hook into such a posi- 

 tion that it catches on a twig the sensitive stalk 



