278 ESSA YS. 



under present opportunities ; and there is reason for thinking 

 that all the prairies east of the Mississippi, and of the Mis- 

 souri up to Minnesota, have been either greatly extended or 

 were even made treeless under Indian occupation and annual 

 burnings. These prairies are flowery with a good number of 

 characteristic plants, many of them evidently derived from the 

 plains farther west. At this season, the predominant vege- 

 tation is of Compositce, especially of Asters and Solidagoes, 

 and of Sunflowers, Silphiums, and other Helianthoid Com- 

 positce. 



The drier and barer plains beyond, clothed with the short 

 Buffalo-grasses, probably never bore trees in their present 

 state, except as now some Cottonwoods (i. e. Poplars) on the 

 margins of the long rivers which traverse them in their course 

 from the Rocky Mountains to the Mississippi. Westward, the 

 plains grow more and more saline ; and Wormwoods and Che- 

 nopodiucece of various sorts form the dominant vegetation, 

 some of tbem sui generis or at least peculiar to the country, 

 others identical or congeneric with those of the steppes of 

 central Asia. Along with this common campestrine vegeta- 

 tion there is a large infusion of peculiar American types, 

 which I suppose came from the southward, and to which I will 

 again refer. 



Then come the Rocky Mountains, traversing the whole con- 

 tinent from north to south ; their flanks wooded, but not richly 

 so, — chiefly with Pines and Firs of very few species, and with 

 a single ubiquitous Poplar, their higher crests bearing a well- 

 developed alpine flora. This is the arctic flora prolonged south- 

 ward upon the mountains of sufficient elevation, with a certain 

 admixture in the lower latitudes of types pertaining to the 

 lower vicinity. 



There are almost 200 alpine Phaenogamous species now 

 known on the Rocky Mountains ; fully three-quarters of which 

 are arctic, including Alaskan and Greenlandian ; and about 

 half of them are known in Europe. Several others are north 

 Asian but not European. Even in that northern portion of 

 the Rocky Mountains which the Association is invited to 

 visit, several alpine species novel to European botany may be 



