THE LEA VES. 1 29 



Some plants develop their lea\es into the form of sacs or 

 pitchers. These ordinarily represent the blade of tlie leaf, 

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

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



Fig. 155.— Pitcher-plant {Sarraiciu'.i purpurfa). Leaf above --1 cut o£f to show 

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



petioled, as in Utricularia (tigs. 3S3, 384) ; or the petiole 

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

 382). A few plants ha^'e their leaves modified so as to ser\'e 

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

 animals (figs. 3S6, 3S7, 3SS). 



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 : 



