[from the text] The present book constitutes the general part of a monograph on Rocky Mountain vegetation which has been under way since 1899. It is hoped that another volume dealing with the details of the development and structure of the climax formations of the Great Plains, Rocky Mountains, and Great Basin may appear subsequently. The general principles advanced here are an outgrowth of the treatment in the "Development and Structure of Vegetation" (1904) and "Research Methods in Ecology" (1905), in which an endeavor to organize the whole field of present-day succession was made for the first time. The studies of the past decade have confirmed and broadened the original concepts, and have led irresistibly to the conclusion that they are of universal application. The summer of 1913 and the spring and summer of 1914 were spent in testing both principles and processes throughout the vegetation of the western half of the continent. The area scrutinized extends from the Great Plains to the Pacific Coast and from the Canadian Rockies to the Mexican boundary. The great climax formations of this region were traversed repeatedly, and their development and relations subjected to critical analysis and comparison.