LEAVES OF WATER PLANTS 125 
problem of avoiding submergence; and the stomata 
are confined to the upper side, which alone is in con- 
tact with the atmosphere. Those water plants which 
Fic. 23.—SPRING SUCCESSION OF LEAVES OF MATURE PLANT OF 
ARROW-HEAD (SAGITTARIA SAGITTIFOLIA). 4, 
raise their leaves into the air, on the other hand, have 
leaves of a variety of shapes, which in most respects 
approach those of land plants. An interesting pro- 
