Deam (1) has shown that the flora of Indiana comprises nearly 2,000 species of which approximately 40% of the native forms are on the limits of their range in Indiana. Friesner (8) has shown that Indiana is a critical botanical area, having approximately 45% of its present-day species on the limits of their range within the state. For the purposes of this paper, such plants are considered to be extraneous species. Apparently, this critical nature of Indiana plant distribution applies to all of the higher types of vegetation: ferns, trees, shrubs, grasses and other herbaceous forms. Lindsey (10) has shown that it applies to the trees, 41% of which are extraneous. The mass distribution of these extraneous tree species lies in three general directions from Indiana, vis., northeast, south and southeast. Trefz (11) has likewise shown that it applies to the shrubs, 56% of which are extraneous, with mass distribution of the extraneous forms lying in four general directions from Indiana, viz., north, northeast, northwest and west in order of decreasing importance from the standpoint of numbers. Deam (1) has shown that the distribution of the total extraneous flora lines in nine directions, viz. (in order of decreasing numbers), north, south, west, southwest, east, Atlantic coastal, northeast, northwest, and southeast.
The present study was undertaken to determine how the grasses fit into this picture.