LEAVES SERVING SPECIAL OFFICES. 117 



blades. When the blossoms develop in spring, these scales grow 

 from beneath, greatly expand, and become obovate or obcordatc 

 petaloid leaves, the brown terminal notch 

 of which is the bud-scale, which was un- 

 able to take part in the vernal growth. 



227. Leaves as Spines. All gradations 

 ma} 7 be found between spiny-toothed leaves 

 (as in Holly), in which teeth are pointed and 

 indurated, and leaves which are completely 

 contracted into a simple or multiple spine. 

 Indeed, such a transition is seen in the Bar- 

 berry, Fig. 234. The foliar nature of such 

 spines is manifest from their position, sub- 

 tending a bud from which the foliage of the 

 season proceeds, and themselves not sub- 

 tended by an}' organ. In some Astragali, 

 the petiole of a pinnate leaf indurates into 

 a slender spine and persists, the leaflets 

 early falling. The spine in Fouquiera is a 

 portion of the lower side of the petiole or 

 midrib, indurated and persistent, the rest 

 of the leaf separating by splitting when it 

 has served its office. 1 



228. Leaves adapted to Climbing. Some plants climb b}- the 

 action of the stem or of cei'tain branches specially adapted to 

 this purpose (99) : others gain the needful i \ 

 support by means of their leaves (101) ; some- M Y*^^\ 

 times by an incurvation of the tips, either of 

 a simple blade as in Gloriosa, or small partial 

 blades, as inAdlumia, and often in Clematis, 

 thereby grappling the support ; sometimes by 

 the petiole making a turn or two around a 

 support (as in Maurandia, climbing Antirrhi- 

 nums, Rhodochiton, and Solanum jasminoides, I 

 Fig. 235) ; sometimes by the transformation 

 of one or more leaflets of a compound leaf 

 into tendrils, as in the Pea and Vetch (Fig. 

 204); sometimes by the suppression of all the ^ 235 



leaflets and the conversion of the whole petiole into a tendril, as 

 in Lathyrus Aphaca (Fig. 219) ; and perhaps by the conversion 



1 Described in Tlantse Wrightianae, ii. 63. 



FIG. 234. A venial shoot of common Barberry, showing a lower leaf in the normal 

 state ; the next partially, those still higher completely, transformed into spines. 



FIG. 235. Solanum jasminoides, climbing by coiling and at length indurating petioles. 



