Although investigations in Botany, governed in a measure by the sparsely settled condition of the regions visited, are but incidental to the systematic purpose of the Survey, which has for its main object the determination of data necessary for the construction of a detailed topographical map, yet it is believed that the material here presented, as the result of examination, by specialists, of large and complete collections, will have its value as a substantial contribution to the knowledge of the Botany of portions of the United States west of the 1OOth meridian and south of the 40th parallel.