DEFICIENCY OF FLESHY STRUCTURE. COMPOUND LEAVES. 157 



the modes in which the repulsive character of some plants is 

 softened down by cultivation. In the Cactus tribe, it would 

 seem as if all the nourishment, which would naturally form 

 leaves, is bestowed upon the stems themselves ; and thus the 

 tufts of prickles already noticed (. 219) are the only indica- 

 tions of their place. These prickles are the woody veins ; which 

 are sometimes seen, in specimens grown in hot-houses in this 

 country, to be converted into true though very minute leaves ; 

 in consequence, probably, of the greater supply of nourishment 

 they receive under such circumstances, than in the dry and sterile 

 situations they frequent in their native climes. 



237. The division of leaves into leaflets may be regarded as 

 taking place upon the same general principle. When a single 

 series of leaflets arises from the midrib, the leaf is said to be 

 pinnate, or winged. But sometimes, instead of leaflets arising 



FIG. 65. PINNATB LEAVES. 



from the midrib, we find secondary veins, from which, as from 

 smaller midribs, secondary leaflets arise. Such are called li- 

 pinnate leaves. The division may go yet further; and the 



FfG. 60. Bl-PINNATK AND Tftl-PINNATK LEAVES. 



secondary veins may give off their branches before any leafy 



