239 



Elodea canadensis Michx. Common on alluvial bottom with 

 Ceratophijllum, especially in quiet waters, but not reaching the 

 surface so generally. It is widely distributed and is next in 

 abundance to the preceding species, though forming a very 

 much smaller proportion of the total vegetation. 



Vallisneria spiralis L. Rare; found only in channels with 

 currents, as at the mouth of Quiver Creek. 



Pontederia cordata L. Common along open places, such as 

 the channels at the head of Quiver Lake and the outlet of Flag 

 Lake, on both alluvial and sandy bottoms. 



Heteranthera graminea Vahl. Creeping along margins of 

 lakes and the river, usually on alluvium. 



Juncus acuminatus Michx. Common in shoal water along 

 sandy shores. 



Typlia latifolia L. Occasional patches found in the swamps 

 and sloughs of the permanent backwaters. 



Sparganium eurycarpum Engelm. Frequent in the margins 

 of lakes and sloughs along channels on sandy and alluvial bot- 

 toms. 



Spirodela pohjrrhiza Schleid. Everywhere in quiet waters, 

 forming in places dense mats upon the surface. Often drifted 

 by wind or current in great windrows along shore. Very com- 

 mon in open water, usually but not always on the surface. 

 Often taken in the plankton with other species of the family. 



Lemna trisulca L. Locally abundant in the more open veg- 

 etation of the backwaters in quiet bays and nooks in both sur- 

 face and deeper waters. Not generally distributed, and less 

 abundant than other members of the family. 



Lemna minor L. Associated with Spirodela but much less 

 abundant. 



Wolffia columbiana Karsten. In surface and deeper waters 

 in both river and backwaters among vegetation and in open 

 water. Frequently taken in the plankton. 



