1. Loams, silts, or clays of the upland or slopes, whether of morainic, dolomitic, or loess origin, were nearly always found to be more acid than the immediate alluvial floodplain soils. The drainage waters were always alkaline. The results of selective leaching of bases are thus nicely emphasized. 2. The dunes nearest the lake are composed of alkaline sands. Farther from the shore where dunes are older, alkalinity is gradually replaced by acidity. Selective leaching seems again to be operative. 3. In the alkaline dunes the peaks and depressions showed no appreciable difference in acidity. When acidity becomes established, the slopes and depressions are more acid than the peaks. The explanation lies perhaps in the differences in moisture and organic content, aeration, leaching, etc. 4. The flat, poorly drained sand soils of Thornton were found to be higher and more consistently acid than any of the three bogs mentioned in this paper. A high water table and consequent poor aeration, together with a poverty of bases, are some of the causative agents. 5. The floating mat stages (excepting locally sphagnum beds, etc.) of bogs and very old soils of bog peat origin gave circumneutral reactions. Only in the hydromesophytic portion of Cowles' bog were acid reactions typical. Even here the acidity was often slight. 6. Soils of high acidity usually showed a diminution below, in some cases becoming actually alkaline at a depth of 3 feet. The underlying strata determine the reactions below. 7. Heavy rainfall, drouth periods, freezing, and thawing caused no important fluctuations in H-ion concentrations in the stations studied. 8. Nearly all of the spring flowers, many ferns, and some hitherto so-called acid soil plants were found growing in soils ranging from definite alkalinity to high acidity. H-ion per se, therefore, is not the main factor in determining the distribution of the species considered. 9. Acid clays or silts and acid sands were characterized by two decidedly different plant associations. Again, certain sands, whether alkaline or acid, had in common many plants not found in acid or alkaline silty or clayey soils.