For many years I have lived on the prairie, where I became familiar with the grasses. Each spring I have been delighted with their renewal of growth in watching the brown landscape of rolling hills become carpeted with green. Year after year, with the progress of the season, I have seen the changing aspects, which, with the coming of autumn, end in the wonderful coloration of the prairie grasses. But the prairie as a whole has seemed a somewhat elusive thing, difficult to visualize, not easy to describe, indefinite and extremely variable in its composition. This vagueness of understanding, I believe, has been shared by other students of prairie. A careful survey of the literature reveals scarcely a single contribution that gives a clear ide...