3'° ECOLOGY. 



show. In this zone occurs the curious Vallesneria spiralis, 

 with its corkscrew flower stem, and various potamogetons. 



476. The visible zones. — In the third zone, or the first one 

 which shows in the picture, are great masses of the arrow-leaf 

 (sagittaria) so variable in the form of its leaves. Next is the 

 fourth zone, made up here chiefly of bullrushes (scirpus), and 

 occasionally are clumps of the cattail flag (typha). Behind 

 this is the fifth zone, only to be distinguished at this distance 

 by the bright flower heads of the boneset (Eupatorium perfolia- 

 tum) and joepye-weed (Eupatorium purpureum), and the blue 

 vervain (Verbena hastata), which occurs on the land. Willows 

 make a compact and distinct sixth zone, while at the right, the 

 oaks on the hillside beyond form a seventh zone, and still 

 farther back is a zone of white pines, making the eighth. 



