54 



LEAF-CLIMBERS. 



Chap. II. 



rather long sub-petioles. The main petiole bends a 

 little angularly downwards at each point where a pair 

 of leaflets arises (see fig. 2), and the petiole of the 

 terminal leaflet is bent downwards at right angles ; 

 hence the whole petiole, with its rectangularly bent 

 extremity, acts as a hook. This hook, the lateral 

 petioles being directed a little upwards, forms an 

 excellent grappling apparatus, by which the leaves 



Fig. 2. 

 A young leaf of Clematis viticella. 



readily become entangled with surrounding objects. 

 If they catch nothing, the whole petiole ultimately 

 grows straight. The main petiole, the sub-petioles, 

 and the three branches into which each basi-lateral 

 sub-petiole is generally subdivided, are all sensitive. 

 The basal portion of the main petiole, between the 

 stem and the first pair of leaflets, is less sensitive 

 than the remain ler ; it will, however, clasp a stick 



