ZONAL DISTRIBUTION OF PLANTS. 309 



two submerged zones, the first one is in the rear of the point 

 from where the photograph was taken, and consists of extensive 

 areas of chara in four to five meters of water. The second zone 



Fig. 259. 

 Sagittaria heterophylla. Often forms a zone just outside of the Sagittaria variabilis. 



then is in the water shown in the foreground of the picture. 

 The plants here are also submerged, or only a small portion 

 reaches the surface of the water, and so the zone does not 



