LEAVES SERVING SPECIAL OFFICES. 



Ill 



subject which has of late become highly interesting belong 

 to physiology, and therefore to the following volume, to which 



all historical references are relegated. Only the morphology of 

 such leaves is here under consideration. 



220. As Ascidia or Pitchers, vessels for maceration, &c. These 

 occur in several widely different 

 families of plants. The commonest 

 are those of the Sarracenias, natives 

 of Atlantic North America. They 

 are evident!}' plryllodia (217), the 

 cavity being a hollowed dorsal por- 

 tion : the wing-like or foliaceous por- 

 tion, alwa}"S conspicuous and forming 

 the ventral border, makes the whole 

 organ or most of it in the earlier 

 leaves of the tubular species. The 

 pitchers of S. purpurea (Fig. 221, 

 225), the only species which extends 

 north of Virginia, are open cups, 

 half filled with water, much of which 

 may be rain, in which abundance of 

 insects are usually undergoing macer- 22.5" 

 ation. In 8. variolaris (Fig. 226), the hooded summit, answer- 

 ing to the blade of the leaf, arches over the mouth in such wise 



FIG 220. Pitchers of Heliamphora; 221. of Sarracenia purpurea ; 222. of Nepenthes. 

 223. A phyllodium of a New Holland Acacia. 224. The same, bearing a reduced com- 

 pound blade. 



FIG. 225. Pitcher-leaves of Sarracenia purpurea ; one of them with the upper part 

 cut away. 



