DISTRIBUTION OF VEGETATION IN UNITED STATES. 85 



16. Palustrine Grasses and Sedges. (Plates 26 and 27.) 



Arundinaria tecta (Walt.) Muhl. 



Dulichium arundinaceum (L.) Britton. 



Spartina michauxiana Hitchk. (=S. cynosuroides (L.) Willd.). 



While not strictly a plant of palustrine habitat, Arundinaria is 

 found in moist alluvial soil and is of interest as one of the largest 

 grasses found in the United States. Dulichium is distributed over an 

 area very similar to that occupied by Sparganium, while Spartina 

 occurs in palustrine situations throughout the northeastern portion 

 of the country from Georgia, Oklahoma, and Wyoming to Canada. 



17. Mistletoes. (Plate 28.) 



Arceuthobium cryptopodum Engelm. ( = Razoumof skya cryptopoda (Engelm.) 



Coville. 

 Arceuthobium americanum Nutt. ( = Razoumofskya americana (Nutt.) Kze.). 

 Phoradendron flavescens (Pursh) Nutt. (including varieties). 

 Phoradendron juniperinum Engelm, 



In view of the fact that the mistletoes are independent of the condi- 

 tions which the ordinary terrestrial plant encounters in its relation to 

 the substratum, a series of four of these plants has been selected for our 

 correlational work. The moisture conditions of the substratum in 

 which these plants grow are doubtless determined in large measure by 

 the moisture conditions that exist for the hosts themselves. Phora- 

 dendron flavescens, together with its varieties, possesses an extremely 

 wide range from the Atlantic to the Pacific throughout the southern 

 half of the United States. The other species that have been used are 

 western in their range, and we have been under the unfortunate 

 necessity of representing their areas of distribution by smooth lines 

 which surround the territory in which they are of scattered occur- 

 rence, chiefly in the forested mountains. 



18. Plants of Northern Transcontinental Range. (Plate 29.) 



Arenaria lateriflora L. ( = Mcehringia lateriflora (L.) Fenzl. 

 Parietaria pennsylvanica Muhl. 

 Cornus canadensis L. 



The two herbaceous plants and the single shrub which form this 

 group extend entirely across the North American continent and range 

 southward to different distances, the southernmost range being that of 

 Parietaria. Cornus is the least southerly in its range in the Eastern 

 States, but is the most southerly in California. Transcontinental 

 ranges of this character are extremely abundant among plants of still 

 more northerly distribution than these, a number of trees and shrubs 

 being found almost continuously from Labrador to Alaska. We are 



