154 



STEMS 



grows less rapidly than before, and the untouched side 

 more rapidly than before. This results in a curve about 



the object touched, just as 

 you noted in the case of 

 root tips. After this, the 

 rest of the tendril begins 

 to curve about the sup- 

 port, until at last the plant 

 is fastened as though by 

 spiral springs. (See Fig- 

 ure 52.) 



Woodbine and some 

 kinds of ivy are common 

 vines, the ends of whose 

 tendrils, instead of twining, 

 develop sucker-like disks. 

 § These sucker-like disks 

 attach themselves firmly 

 to walls or to the trunks of 

 trees ; so firmly , in fact, 

 that when you try to pull 

 them off the tendril breaks 

 and leaves the suckers At- 

 tached to the surface of 



Fig. 52. - The curving tendrils of the star ^j^g support. It is evident 

 cucumber vine. 



that this manner of climb- 

 ing is particularly well suited for vines which grow on walls. 



D. Exceptional Forms of Stems. — The branches of 

 stems usually resemble in structure the stems from which 

 they arise, but there are some striking exceptions. 



The plant commonly called smilax, or wedding smilax. 



