ECOLOGY 79 



the level of the surface. There can be no question of mutual 

 shading and none of the considerations which gave advantage 

 to the form of the submersed leaf can here apply. 



FIG. 38. A xerophytic habit of the prickly lettuce, Lactuca scariola. View 

 as seen from the east. 



190. A few plants are capable of growing either entirely 

 under water or with at least some of the leaves entirely above 



