62 PRACTICAL BOTANY 



Tendril climbers attach themselves to the stems or branches 

 of other plants or to inanimate objects by means of special, 

 slender, thread-shaped, leafless organs called tendrils. These 

 are modified leaves or parts of a leaf, as in the pea (Fig. 306) ; 

 or modified branches, as in the grape, the Virginia creeper 

 (Fig. 48), and the passion flower. When a living and active 

 tendril comes into contact with a support, this contact causes 

 growth to take place more rapidly on the exterior side of the 



FIG. 49. A tropical Smilax, a tendril climber 



a, tendril coiled about a portion of the stem ; I, tendril coiled about a leafstalk ; 

 br, a young branch ; t, young unattached tendrils 



tendril (that side which does not touch the foreign object), 

 and thus the tendril is made to coil about the support. The 

 sensitiveness of some tendrils is almost inconceivably great. 

 Those of the star, wild, or bur cucumber (Sicyos) are stimu- 

 lated to curve by a moving weight of I-Q-^-Q-Q-Q of a grain, or 

 one eighth of the smallest amount which can be perceived 

 by the most sensitive part of the human skin (the face). 

 After a tendril has become attached the free portions are also 

 thrown into coils and thus the plant is drawn closer to the 

 support. As a result of its attachment the tendril becomes 

 stronger and often considerably thicker. In some plants, 

 as the Virginia creeper, the tendrils are enabled to fasten 



