241 



Eleocharis acicularis R. Br. Common in shallow water on 

 alluvial and sandy bottoms. 



Scirpus pungens Vahl. Common along sandy margins. 



Scirpus lacustris L. Lake and swamp margins ; common 

 on both sandy and alluvial bottom. 



Scirpus smith ii Gray. Occasional along sandy shores. 



Scirpus fiuviatilis Gray. Very abundant in bottom-land 

 swamps on alluvial bottom. Forming great tracts, to the ex- 

 clusion of other plants, and contributing largely to the decay- 

 ing vegetation of the backwaters. 



Scirpus atrovirens Muhl. Common, in marshy borders. 



Rhynchospora alba Vahl. Rare, along sandy margins of 

 backwaters in shallow water. 



Zizania aquatica L. Forming meadows of considerable ex- 

 tent in margins of lakes and more open swamps in the backwaters. 



Equisetum lime-sum L. Sparingly present along springy 

 margins of sandy shores. 



Azolla caroliniana Willd. This brilliant little cryptogam 

 is locally abundant in warm sheltered regions of the back- 

 waters in early summer. It is found principally in the dense 

 mats of drifted Spirodela, where it forms bright red rosettes, 

 the clusters sometimes forming an area several square feet in 

 extent.^ 



The filamentous algae, principally Spirogyra and Zygnema, 

 becomes very abundant in shallow waters in spring and early 

 summer as the bottom-lands emerge from the receding flood. 

 As the shores of the more permanent bodies of water are left 

 bare, there remains upon them, half supported by the semi- 

 aquatic vegetation, a thick felted mat of fading green, the 

 strength and consistency of which are sufficient to justify the 

 local name of "blanket moss." Its rapid decay in warm shal- 

 low water contributes immediately to the support of the plank- 

 ton. 



VEGETATION AT THE SEVERAL STATIONS. 



Illinois Bicer (Station E). — The following statements con- 

 cerning the vegetation of the river are based upon many obser- 



