THE STEM AND THE LEAF 5 
The development and mode of operation of tendrils is espe- 
cially interesting (figs. 58 and 59). The tendril is either a 
leafless, thread-like branch, as in the grapevine, or a highly 
modified leaf or part of a leaf, as in the cucumber. When a 
living and active tendril comes into contact with any suitable 
Fie. 58. Bur cucumber (Sicyos), a tendril climber 
At a, b, ce, d, e, and f successive stages in the history of tendrils are shown. The 
tendril, at first curved, becomes straighter, then curls up at the tip, and finally 
(after becoming attached to some object) coils itself into a close spiral and thus 
draws the plant with considerable force toward the sustaining object 
support for the climber, this contact brings about more active 
growth on the exterior side of the tendril (that side which 
does not touch the foreign object). In this way the tendril 
is made to coil about the support. Soon after the tendril has 
become attached, the free portions are thrown into coils, and 
the shortening which results draws the stem of the climber 
closer to the support. 
