MODIFICATIONS OF FORM 



183 



parts of the lower region of the leaf may be prehensile, while the 

 lamina or pinnae develop normally after the lower region has grasped 

 the support, as in Corydalis, Clematis, and Solanum jasminoides ; or 

 lateral " stipular " structures may be represented by tendrils, as in 

 Smilax ; or again, the tendril may be referable to a whole shoot, as 

 in the Grape- Vine ; and probably a like interpretation may be 

 applied to those of the Passion Flower and the Cucurbits. Thus 

 various parts of the shoot, or the whole of one, may in different cases 

 develop as structures called tendrils, and act as prehensile organs. 



FIG. 136. 



Portion of stem of Sicyos, a Cucurbit, with tendril attached to support. #=point 

 of reversal of the coiling of the tendril. See Text. (After Strasburger.) 



<* 



Once they are attached, tendrils strengthen their tissues. As 

 growth ceases, the part between the distal attachment and the base 

 is usually thrown into spiral curves ; and as both ends are fixed, these 

 are necessarily equal in number in reverse directions. The elastic 

 tissues of the spirally coiled tendril act like a spring in resisting wind, 

 and recover when the pressure is relieved (Fig. 136). 



Adhesive Climbers attach themselves by application of some part 

 of their surface very closely to the surface of the support, following 

 its minute irregularities. The result is that they are affixed so closely 

 that they will often break before quitting hold. Roots require little 

 adaptation to this function. The Ivy is a native type of a number of 

 plants of other lands, often large and woody, which attach themselves 

 in this way to tree-trunks, rocks, etc. Such roots of attachment are 

 " adventitious," that is, they are formed not from the root-system, 



