1900] FLORA OF THE WHITE LAKE REGION 435 
higher than the pines and the most common oaks in their per- 
centage of ash, but they, too, are much less common, often 
wholly absent from large areas. In general, analyses seem to 
show a smaller percentage of ash in the same species when 
growing on sandy or gravelly soil than on soils stronger in such 
mineral ingredients as the trees use, like clay, clay-loam, or lime 
soils. 
But alongside of mineral constituents certain physical condi- 
tions are equally important or indispensable. The ability to 
reach and appropriate what is provided must exist. Porosity, 
depth of soil, moisture, here come into play. The last is the 
most important of all in soil conditions, since vegetable life is 
impossible without some degree of it. For porosity sand ranks 
the highest, in capability of retaining water it is the lowest, clay 
being the highest; in capacity for condensing moisture from the 
air, it is likewise the least powerful, humus and clay being best. 
In discussing such matters as these, Schlich well states what 
must have become evident to any who have made a comparative 
Study of the vegetation of the dunes and of the bordering region. 
Though written with reference to cultivated woods it is as true 
of the natural forests. ‘Woods thrive equally well on soils of 
the most different geological origin, while great differences exist 
in the development of the same species if grown on soils of the 
Same geological origin. The phenomena are explained by the 
great importance of the physical qualities of the soil, depth, por- 
Osity, and a proper degree of moisture’” These conditions go 
far toward explaining the differences in vegetation seen on the 
Opposite sides of White lake and in corresponding regions, for 
they are true of vegetation as a whole as well as of the trees. In 
the case of the trees it was a “mixed wood,” but a “mixed 
wood” of much greater variety on the south side where the 
Physical constitution of the soil as well as its chemical ingre- 
dients furnished a more suitable habitat. Though it was through- 
Sut a dune formation superposed on a clay substratum, the 
_ Telations of the vegetation to the substratum were also most 
* Manual of Forestry 1: 143. 1889. 
