THE LEAVES. I05 



as foliage. For example, the petiole may be made sensitive 

 to contact, and adapted to wrap about slender objects, like 

 a tendril, as in clematis and nasturtium (fig. 100). Such 

 plants are called leaf-climbers. 



Some plants develop their leaves into the form of sacs or 



Fig. 98. Fig. gg. 



Fin 98.— Parallel venation of leaf of Polyganatum latifolium. Natural size.— After 



Fig. gg.— Pinnately netted venation of leaf of a willow. Natural size.— After Ettings- 

 hausen. 



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. loi); or 

 petioled, as in Utricularia (figs. 221, 222); or the petiole 



