NORTH AMERICAN FLORA. 217 



Laurels) even become forest trees in some places ; more com- 

 monly they are shrubs, forming dense thickets on steep moun- 

 tain-sides, through which the traveler can make his way only 

 by following old bear-paths, or by keeping strictly on the di- 

 viding crests of the leading ridges. 



Only on the summits do we find Rhododendron Cataw- 

 biense, parent of so many handsome forms in English 

 grounds, and on the higher wooded slopes the yellow and the 

 flame-colored Azalea calendulacea ; on the lower, the pink 

 A. nudiflora and more showy A. arborescens, along with the 

 common and widespread A. viscosa. The latter part of 

 June is the proper time to explore this region, and, if only 

 one portion can be visited, Roan Mountain should be pre- 

 ferred. 



On these mountain-tops we meet with a curious anomaly in 

 geographical distribution. With rarest exceptions, plants 

 which are common to this country and to Europe extend well 

 northward. But on these summits from southern Virginia to 

 Carolina, yet nowhere else, we find — undoubtedly indige- 

 nous and undoubtedly identical with the European species — 

 the Lily-of-the-Valley ! 



I have given so much of my time to the botany of the At- 

 lantic border that I can barely touch upon that of the western 

 regions. 



Between the wooded country of the Atlantic side of the 

 continent and that of the Pacific side lies a vast extend of 

 plains which are essentially woodless, except where they are 

 traversed by mountain-chains. The prairies of the Atlantic 

 States bordering the Mississippi and of the Winnipeg country 

 shade off into the drier and gradually more saline plains, which, 

 with an even and gradual rise, attain an elevation of 5000 feet 

 or more where they abut against the Rocky Mountains. Until 

 these are reached (over a space from the Alleghanies westward 

 of about twenty degrees of longitude) the plains are unbroken. 

 To a moderate distance beyond the Mississippi the country 

 must have been in the main naturally wooded. There is rain- 

 fall enough for forest on these actual prairies. Trees grow 

 fairly well when planted ; they are coming up spontaneously 



