174 



OEGANOGEAPHY. 



Solatia the spines are situated on the surface of the blade ; while 

 in the Barberry {fig. 357) the blade has little or no parenchyma 

 produced between its veins, which are of a spiny character, so that 

 the whole blade becomes spinous. These spines may be readily 

 distinguished from those already described which are modified 

 branches, because in the latter ease they always arise from the 

 axil of the leaf, instead of from the leaf itself. Spines may 

 also be readily distinguished from prickles by their internal 

 structm^e and the other characters alluded to when speaking of 

 the spines of branches. 2nd, The petiole may assume a spiny 

 character, either at its apex, as in Astragalus Tragacantha and 

 A. massiliensis ; or at its base by the pulvinus {fig. 358), as in 

 Ribes Grossularia. And, 3rd, The stipules may become trans- 

 formed into spines, as in the False Acacia {Robinia pseudo- 

 acacia), {fig. 249). 



Tendrils of Leaves. — Any part of the leaf may also become 

 cirrhose or transformed into a tendril. Thus, — 1st, The midrib 

 of the blade of a simple leaf may project beyond the apex, 

 and form a tendril, as in Gloriosa su^crba ; or in other cases 



Fig. 359. 



Fig. 361. 



Fig. 360. 



Fig. 359. Leaf o{ Lathyrus, s>iowing a winged petiole, with two half- 

 sagittate stipules at its base, and terminated by a tendril.^— FiV?. 360. A 

 portion of the stem of Lathyrus Aphaca, with stipules, s s, and cirrhose 



tendril, v. Pig, 861. A portion of the stem of Smilax, bearing a petio- 



late leaf, and two tendrils in place of stipules. 



some of the leaflets of a compound leaf may become trans- 

 formed into branching tendrils {figs. 351 and 359), as in 



