THE LEAVES. 



129 



Some plants develop their leaves into the form of sacs or 

 pitchers. These ordinarily represent the blade of the leaf, 

 and are more or less urn- or trumpet-shaped. They may be 

 either without petiole, as in Sarracenia (fig. 155) ; or 



k«^W 



Fig. 155. — Pitcher-plant (Sarracenia purpurea). Leaf above A cut off to show 

 trumpet form. One-third natural size. — After Gray. 



petioled, as in Utricularia (figs. 383, 384) ; or the petiole 

 may be winged to serve for foliage, as in Nepenthes (fig. 

 382). A few plants have their leaves modified so as to serve 

 as traps, which, by their sudden movements, capture small 

 animals (figs. 386, 387, 388). 



But generally the foliage function is subordinated to the 

 other work, and the leaf takes on peculiar forms, the more 

 important of which are as follows : 



