74 



FOUNDATIONS OF BOTANY 



(3) Twining about any slender upright support, as 

 shown in Fig. 42. 



89. Tendril-Climbers. — The plants which climb by 

 means of tendrils are important subjects for study, but 

 they cannot usually be managed very well in the school- 

 room. Continued observation soon shows that the tips of 



tendrils sweep slowly about in 

 the air until they come in contact 

 with some object about which 

 they can coU. themselves. After 

 the tendril has taken a few turns 

 about its support, the free part of 

 the tendril coils into a spiral and 

 thus draws the whole stem tcnvard 

 the point of attachment, as shown 

 in Fig. 40. Some tendrils are 

 modified leaves or stipules, as 

 shown in Fig. 104 ; others are 

 modified stems. 



90. Twiners. — Only a few of 

 the upper internodes of the stem 

 of a twiner are concerned in pro- 

 ducing the movements of the tip 

 of the stem. This is kept revolving in an elliptical or 

 circular path until it encounters some roughish and not too 

 stout object, about which it then proceeds to coil itself. 



The movements of the younger internodes of the stems 

 of twiners are among the most extensive of all the move- 

 ments made by plants. A hop-vine which has climbed to 

 the top of its stake may sweep its tip continually around 

 the circumference of a circle two feet in diameter, and the 



Fig 40. — Coiling of a Tendril 

 of Bryony. 



