236 A NATURALIST IN THE GREAT LAKES REGION 



It bears a few, short, threadlike roots. The surface of the pond 

 is often completely covered with this duckweed. 



Many plants root in the soft bottom and grow more or less 

 submerged ; such are pondweed, Potamogeton of several species, 

 as P. natans, P. crispus, P. pectinatus, P. lucens, P. zosteri- 

 folius; water milfoil, Myriophyllum; hornwort, Ceratophyllum; 

 water weed, Elodea; tape grass, Vallisneria; bladderwort, Utri- 

 cularia; water buttercup, Ranunculus aquatilis (Fig. 64). 



FIG. 335. The bulrush zone, Galien River, New Buffalo, Michigan 



Pondweed (Fig. 326) roots at the bottom of the pond and 

 sends up its leafy stalk to the surface. Some of the leaves may 

 lie on the surface of the water. Such are usually fairly firm 

 and broad, while the submerged leaves are commonly narrow, 

 translucent, and fragile. Potamogeton natans has egg-shaped 

 floating leaves i inch or more long and very narrow, submerged 

 ones less than .1 of an inch wide. P. crispus has only submerged 

 leaves which are lance-shaped and are borne on short stems. 

 The margins of the leaves are finely saw-toothed and crinkly. 



