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 coil 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 toward 
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 
Fi¢ 40.—Coiling of a Tendri). Of a twiner are concerned in pro- 
Shia 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 
