20 BOTANICAL GAZETTE [SEPTEMBER 
syluanicum, V. vacillans, with considerable Gaylussacia baccata. 
On the whole, the Pferis communities are more characteristic of 
the portion of the ridge area west of the Platte River and the 
Vaccinium of that east of the river. No definite factors determining 
the distribution of these communities have yet been established. 
The Pleris seems to be more moisture-requiring than the Vaccinium, 
and it certainly grows more luxuriantly in the moister habitats 
(fig. 9). The Vaccinium species are usually regarded as more acid- 
tolerant, and investigations along these lines may. yield definite 
results. ' 
BEECH-MAPLE-HEMLOCK STAGE.—It is generally recognized 
throughout Michigan that the deciduous hardwood forest is con- 
fined to rich clay or loamy soil, white pine forests are found on 
sandy loam, and the pioneer conifers on poor sandy soil. The 
development of a climax deciduous forest on fixed dunes, as found 
in the Point Betsie region and at other points along the Michigan 
shore, is an interesting problem, the solution of which should 
materially be aided by the evidence to be obtained from a study 
of this relatively untouched region. As suggested by the preceding 
morphological study, the climax forest which developed on the 
morainic upland has begun to invade the sand ridge area along all 
lines of contact between the moraines and the sand, the under- 
growth having gone farthest, and the tree species migrating more 
slowly. The first tree of the climax forest to appear in the sand 
ridges is Tsuga canadensis, scattered specimens of which are found 
up to a quarter or half a mile from the morainic border in the tension 
zone on the west, and for varying distances on the other borders of 
the sand ridge area. Many parts of the lowland border on the 
south have been cleared of trees, but in the small triangle between 
Long and Rush Lakes the deciduous forest is in contact with a 
cedar swamp, and we can find there a horizontal succession in 
practically untouched condition. The first hardwood pioneers in 
the swamp are Fraxinus americana, F. nigra, Ulmus americana, 
Tilia americana, and Acer rubrum. As Thuja disappears, the trees 
of the beech-maple-hemlock forest begin to come in on an alluvial 
substratum, forming a lake plain washed down from the Algonquin 
