542 Part IV. Chapter 3. 
Zannichellia palustris, Zygnema cruciatum and species of Chara showed the 
following algae'). 
Chroococcaceae. 
Merismopedia glauca Naeg. | Chroococus cohaerens Naeg. 
> violacea Breb. | 
Nostocaceae. 2 
Oscillaria (several species). | Nostoc pruniforme Ag. Be 
i 
Palmellaceae. E 
Scenedesmus caudatus Corda. Raphidium polymorphum Fres. @ 
» dimorphus Kg. Polyedrium trigonum Naeg. var. punc- = 
tatum Kirch. ee 
Scenedesmus obtusus Meyen. Protococcus viridis Ag. © 
Pediastrum angulosum Ehr. Euglena viridis Schrank. Sn 
> Boryanum Turpin. = 
Desmidiaceae. 5 
Docidium baculum Breb. Cosmarium pulcherrimum Nord. 
Cosmarium bioculatum Breb. » undulatum Corda. 
» conspersum Ralfs. Euastrum verrucosum Ehrb. ® 
> Meneghinii Breb. Staurastrum gracile Ralfs. = 
>  nitidum De Not. » polymorphum Breb. 3 
Diatomaceae. 2 
Cymbella gastroides Kutz. Gomphonema constrictum Ehrb. = 
Navicula viridis Ehr. var.amphigompus | Cocconeis pediculus Ehr. > 
» major Kutz. Ehr. | Epithemia gibba Kutz. | 
» producta W. Sm. » turgida Ehr. 
Pleurosigma intermedium W. Sm. Synedra ulna Nitsch. &: 
Gomphonema clavatum Ehr. Fragilaria Harrisonii W. Sm. a 
Melosira varians Ag. 
} 
I 
\ 
Sr ec 
Ze ae CHR EEE 
a N a a 
6. The intruding Forests of the Foothills. 
The Great Plains have no indigenous forest flora, but the trees have been 
derived from two sources of supply the forests of the Mississippi basin and e: 
the forest of the Rocky Mountains represented in the foot-hills. The two . 
elements as previously described meet in the valley of the Niobrara where 
according to BESSEy Juglans nigra and Pinus ponderosa var. scopulorum mingle. 
The deciduous leaved forest trees are found in their most typic forms 
only along the large rivers. Their extension eastward has followed the water 
I) WEBBER, H. J.: The fresh-water Algae of the Plains. American Naturalist XXIII (1889): 
1011—1013. 
