SECTION 6.] 



STEMS. 



41 



93), as also the shorter ones of the Japanese species, effect the object differ- 

 ently, namely, by expanding the tips of the tendrils into a flat disk, with 

 au adhesive face. This is appKed to the supporting object, and it adheres 



firmly ; then a 

 shortening of 

 the tendril and 

 its branches by coiling brings up the growing 

 shoot close to the support. This is an adapta- 

 tion for climbing mural rocks or walls, or the 

 trunks of trees, to which ordinary tendrils are 

 unable to cling. The Ivy and Poison Ivy attain 

 the same result by means of aerial rootlets (78). 



100. Some tendrils are leaves or parts of 

 leaves, as those of the Pea (Pig. 35). The nar 

 ture of the tendril is known by its position. A 

 tendril from the axil of a leaf, like that of Pas- 

 sion-flowers (Pig. 92) is of course a stem, i. e. 

 a branch. So is one which terminates a stem, 

 as in the Grape- Vine. 



101. Spines or Thorns (Pig. 95, 96) are 

 commonly stunted and hardened branches 

 or tips of stems or branches, as are those of 

 Hawthorn, Honey-Locust, etc. In the Pear 

 and Sloe all gradations occur between spines 

 and spine-like (spinescent) branches. Spines 



may be reduced and indurated leaves ; as in tlie Barberry, where their 

 nature is revealed by their situation, underneath an axillary bud. But 



Fio. 92. A small Pa.s.sion -flower (Passlflora sicyoides), sliowing the tendrils. 



Fig. 93. Piece of the stem of Virdnia Creeper, bearing a leaf and ». tendril. 

 9-1. Tips of a tendril, about the natural .size, showing the disks by which they hold 

 fast to walls, ete. 



