Date of this Version
While carrying on a study of the plant formations and associations of semi-arid southeastern Washington in 1912-1914, it soon became apparent that for a proper understanding of the development and structure of these associations a knowledge of the root-systems of the more important prairie species was imperative. Consequently, during the fall, winter, and spring of 1913--1914, more than 350 root-systems of 25 of the most important ecological species were examined. This paper contains descriptions of these, together with a discussion of the conditions under which the plants grow.
The prairies of southeastern Washington, and their eastward extension into adjacent Idaho, occupy a position between the foothills of the Bitterroot Mountains on the east, and the sagebrush region of western Adams, eastern Franklin, and western Walla Walla counties, Washington, on the west, On the south they are bounded by that high upfold of the lava-rock known as the Blue Mountains. Northward the Spokane gravels, extending somewhat southward of Spokane, with their open growth of yellow pine, mark at once the general northern boundary of the exposed part of the great lava sheet and its accompanying prairie formation. As the great Columbian Plateau with its wind-moulded hills ascends to an altitude of 2700 feet near its eastern border, the precipitation correspondingly increases, and this reflects itself in a more highly developed type of prairie vegetation. In fact, the well-developed high prairies occupy a relatively narrow belt of 30-50 miles in diameter along the eastern edge of the plateau, while the area westward is characterized by a very open type of Bunchgrass vegetation. Pullman, Washington, the base station, where these studies were carried on, lies 85 miles south of Spokane and in the midst of the best developed type of prairie.