NORTH AMERICAN FLORA. 2TT 
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 extent 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 
