Climbing Plants 237 



first-formed joints, or " internodes," of the stem are 

 straight, and stand erect and still. "But the next 

 formed," says Darwin, "whilst very young, may 

 be seen to bend to one side, and to travel slowly 

 around toward all points of the compass, moving 

 like the hands of a watch, with the sun." The 

 movement very soon acquires its full ordinary ve- 

 locity, and it continues as long as the plant con- 

 tinues to grow; but each separate internode, as 

 it becomes old, ceases to move. The internodes 

 travel slowly when they are very young, and ac- 

 celerate their speed as they approach maturity. 



So the tender tip and the lower and older part 

 of the spray are moving in the same direction, 

 but at varying rates ; and this difference some- 

 times gives a serpentine twist to the shoots of 

 vigorous twiners. The ends of many vine-sprays 

 are bent over so as to form hooks, which are of 

 great assistance to the plants in their efforts to rise 

 in the world. For not only does the terminal 

 hook lay hold of any support within reach, but it 

 causes the tip of the shoot to embrace this sup- 

 port much more closely than it could otherwise do, 

 and thus may prevent the stem from being blown 

 aside in windy weather. It is very noticeable in the 

 young sprays of the Virginia creeper (see Fig. 67). 



