The tall-grass prairies of the central United States have long been the object of considerable interest, study and speculation. Transeau (1935) summed up the literature and the problems of the Prairie Peninsula with a number of questions, most of which are still debatable, at least as they pertain to specific areas in the borders of the region. Curtis and Greene (1949) reported on a presence study of remnant prairies in Wisconsin and Curtis followed this (1955) with the continuum study which reported one phase of the broad phytosociological study of native vegetation types being carried on at the University of Wisconsin. This latter study showed prairies scattered through roughly the southwestern onethird of the state; Curtis concluded that the variations among these prairies as a whole represented one continuous gradation based primarily on soil moisture. He did not make any comment regarding the factors involved in the distribution of prairie vs. forest in Wisconsin, nor did he discuss any possible distinction between different geographical regions within the area of his study. The existence of the main body of the prairie peninsula, probably including the largest prairies of southern Wisconsin, appears to be controlled primarily by a complex of climatic factors, especially extremes of moisture, as discussed by Transeau (1935). However, the transition of one climatic region to another, in the absence of strong topographic features, should be relatively smooth and gradual, whereas the transition zone of prairie to forest vegetation on the northeast and southeast sides of the prairie peninsula is a wide, complexly intermingled mosaic, with boundaries of each vegetation type usually distinct and abrupt (cf. Curtis 1955, and Transeau 1935). Therefore compensating factors apparently must be sought to explain the existence and persistence of these prairie island outliers in the forest matrix. One of the larger of these prairie island areas in Wisconsin is that lying in Racine and Kenosha counties, in the southeastern corner of the state, separated from the main body of prairies southward and westward by the wooded slopes of the Fox River valley. This area is roughly 20 x 25 miles across and, again, is not pure prairie but a large prairie matrix in which several islands or fingers of forest occur on the better-drained moraine slopes and stream valleys. An intensive study of the remnant prairies in this area was begun in 1954 in the hope of discovering whether this extension of the prairie differed from other prairies in its species composition and to see whether any particular factors could be found to explain both its presence and its differences, if any. Topographically the area is a gently rolling ground moraine lying between 650 and 750 feet above sea level (70-170 feet above Lake Michigan). It is so nearly level that in several places there is less than 20 feet per mile difference in elevation as seen on the U. S. Geological Survey topographic quadrangle maps. Soils here are chiefly of the Elliott-Ashkum series, rather heavy clays with poor internal drainage. Rainfall at Milwaukee and Chicago weather stations is about 30 inches per year, which seems adequate for the forest areas in and around this prairie; in fact, this prairie approached within ten miles of one of the best stands of native beech along Lake Michigan, indicating an extreme narrowing of the prairie-forest ecotone which is probably a result of the influence of the lake (Salamun and Whitford, 1954).