APPENDIX TO REPORT OF THE SECRETARY. 63 



examinations extended over a great portion of Colorado, Wyoming, Utah 

 Nevada, and California. Their investigation into the Alpine floras and 

 tree-vegetation of the Eocky Mountains and Sierra Nevada enabled them 

 to give a clear idea of the relations and influence of the climatic condi- 

 tions on both sides of the great mountain-ranges. 



Sir Joseph Hooker, whose botanical researches embrace the greater 

 part of Europe ; the Indies, from the Bay of Bengal across the Hima- 

 laya's to Thibet ; the antarctic regions and the southern part of South 

 America, New Zealand, Australia, South Africa, Morocco, and Asia 

 Minor, presents in the English periodical " Nature," for October 25, 1877, 

 an outline of his studies during the season, and this outline, when filled 

 out, will form a most important part of the eleventh annual Eeport of the 

 Survey. It will be seen at a glance that the report will be of the most 

 comprehensive character, and cannot fail to be of the highest interest 

 to our people. The tree-vegetation, and especially the coniferae, were 

 made special objects of study, and many obscure points were cleared up. 



Dr. Hooker sums up the results of the joint investigations of Dr. Gray 

 and himself, aided by Dr. Gray's previously-intimate knowledge of the 

 elements of the American flora, from the Mississippi to the Pacific coast : 



That the vegetation of the middle latitudes of the continent resolves itself into three 

 principal meridional floras, incomparably more diverse than those presented by any 

 similar meridians in the Old World, being, in fact, as far as the trees, shrubs, and many 

 genera of herbaceous plants are concerned, absolutely distinct. These are the two 

 humid and the dry intermediate regions above indicated. 



Each of these, again, is subdivisible into three, as follows : 



1. The Atlantic slope plus Mississippi region, subdivisible into (a) an Atlantic, (/3) 

 a Mississippi Valley, and (y) an interposed mountain region with a temperate and sub- 

 alpine flora. 



2. The Pacific slope, subdivisible into (a) a very humid, cool, forest-clad coast range; 

 (/3) the great, hot, drier Californian valley formed by the San Juan River flowing to 

 the north and the Sacramento River flowing to the south, both into the Bay of San 

 Francisco; and (y) the Sierra Nevada flora, temperate, subalpine, and Alpine. 



3. The Rocky Mountain region (in its widest sense extending from the Mississippi 

 beyond its forest region to the Sierra Nevada), subdivisible into (a) a prairie flora, 

 (,3) a desert or a saline flora, (y) a Rocky Mountain proper flora, temperate, subalpine, 

 and Alpine. 



As above stated, the difference between the floras of the first and second of these re- 

 gions is specifically, and to a great extent generically, absolute; not a pine or oak, 

 maple, elm, plane, or birch of Eastern America extends to Western America ; and genera 

 of thirty to fifty species are confined to each. The Rocky Mountain region again, though 

 abundantly distinct from both, has a few elements of the eastern region and still more 

 of the western. 



Mauy int-eresting facts connected with the origin and distribution of American plants, 

 and the introduction of the various types into three regions, presented themselves to 

 our observations or our minds during our wanderings. Many of these are suggestive of 

 comparative study with the admirable results of Heer's and Lesquereux's investiga- 

 tions into the Pliocene and Miocene plants of the north temperate and frigid zones, 

 and which had already engaged Dr. Gray's attention, as may be found in his various 

 publications. No less interesting are the traces of the influence of a glacial and a 

 warmer period in directing the course of migration of arctic forms southward and 

 Mexican forms northward in the continent, and of the efi'ects of the great body of 



