240 



Wolffia braziliensis Weddell. With the preceding but less 

 abundant.* 



Sagittaria variabilis Engelm. Abundant in shallow water 

 along margins of lakes and swamps and in protected nooks 

 along the river. On both alluvial and sandy bottoms, and often 

 forming well-defined belts of vegetation. 



Triglochin palustris L. Occasionally found in marshes on 

 alluvium. 



Potamogeton nutans L. Widely distributed along margins 

 of lakes, sloughs, and the river, in both quiet and flowing 

 water, often occupying the open spaces in the littoral vegetation 

 and among Ceratophyllum and Elodea. 



Potamogeton pus illus L. Rare, in open water of larger lakes. 



Potamogeton pectinatus L. Rare, in lakes and in river near 

 channels where there is considerable current. 



Naias flexilis var. robusta Morong. Frequent along shores 

 of lakes and river in shallow water on alluvium. 



Dulichium spathaceum Pers. Occasionally found along allu- 

 vial shores of quiet backwaters. 



Eleocharis palustris R. Br. Very common, forming patches 

 of considerable extent along low sandy shores and in the mar- 

 gins of swamps. 



Eleocharis intermedia Schultes. Occasional in the mar- 

 gins of lakes and swamps. 



Eleocharis tenuis Schultes. In shallow water in margins 

 of swamps. Not common. 



♦According to some criteria all of our representatives of the Lemnacecz might be 

 considered as part of the plankton. This is especially true of Wolffia, which is found 

 in open water at all levels. Wind and current have much to do with its distribution, 

 but, it has, nevertheless, a limnetic habit, comparable with that of many organisms of 

 the plankton. Its general distribution and its small size afford further reason for 

 regarding it as a part of the plankton of our locality. It was therefore not removed 

 before measurement of the plankton. There are but few instances in our collections 

 where it becomes a disturbing factor by reason of its predominance. The other 

 members of the family are much larger and are more irregular in their distribution, 

 and thus tend to distort the quantitative relations of the more typical plankton. For 

 these practical reasons it seemed best to remove all specimens of these species from 

 our catches before measurement. 



