270 FORESTS AND TREES OF NORTH AMERICA. 



and several pines are found. Two willows have as yet been found only 

 in it. One pine is believed to be more common here than elsewhere. 3 



In the four last regions the place of forests is also supplied by nu- 

 merous peculiar shrubs, mostly very distinct from any of the trees, as 

 well as from the chapparal of Mexico, though some of the same genera 

 appear as in the latter. These are not all stunted trees, but of entirely 

 different families, and formed especially for the arid regions they in- 

 habit. R, S, T, U, V, together, form a peculiar province, which may 

 be distinguished as the Rocky Mountain Province. 



W, the Californian region, is the most highly favored of the western 

 groups in the variety, though not of the extent of its forests, which 

 are confined chiefly to the mountains, while most the species occur 

 in groups, scattered singly through the prairie. Eighteen trees are 

 considered characteristic, and e{(//i^eew peculiar; making, in all, - 36 



Seven others are found near San Diego, and are probably charac- 

 teristic of Lower California. 



X, the Oregonian, is densely wooded over nine-tenths of its surface, 

 prairies occurring chiefly in the valleys of the southern part, and 

 gradually disappearing towards the north. Thirteen trees are considered 

 characteristic, and nine peculiar, though the unexplored character of the 

 regions northward may make the number larger than it really is, 22 



Y, the Kootanic region, is described as very densely wooded almost 

 everywhere, and certainly that part which extends south of latitude 

 49° is covered with forests almost equal in size and density to those of 

 the Oregonian. Eight trees are believed to be among those character- 

 istic of it, and some will probably be found peculiar. - - 8 



Z, the Yukon region, is believed to be generally wooded, but almost 

 nothing is known of it or its peculiar products. Some trees have been 

 found as far north as Kotzebue's Sound, (2) the northern limit of trees 

 which are not known farther south, but may be Asiatic, Six of those 

 in the catalogue are attributed to this region, as they are found only 

 as stragglers within the boundary of the United States. - - 6 



The trees of the western regions (including the Mexican boundary 

 group) are, therefore, 131 species. The great wooded regions of the 

 northwest — X, Y, and Z — apparently form a province distinct from 

 those east or south of them. 



W partakes of the characters of those of Lower California and Ari- 

 zona, and with the former may form a province to be called the 

 Nevadian. Further exploration is, however, necessary to decide their 

 mutual relations. 



Although neither time nor space will permit here a full statement 

 of the grounds on which the dividing lines are laid down, yet a short 

 statement of the principal ones will be necessary, in order to enable 

 observers to collect and increase information on this interesting branch 

 of Physical Geography. Trees represent only certain families and 

 genera of plants, and their distribution alone would not, therefore, 

 indicate that of other plants and of animals; but forests have a won- 

 derful influence on both, and it is well known ito naturalists that neither 

 rivers, lakes, nor mountains separate the range of so many species as 

 the line where a continuous forest skirts a woodless country. 



The full line 1 — 2, broken towards the west, shows the northern 



