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 ^ suppor t. 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, 



