16 BOTANICAL GAZETTE [SEPTEMBER 
this region Decodon is chiefly confined to streams, as it has been 
observed on lakes or ponds in only one or two instances. 
VEGETATION OF MORAINIC UPLANDS.—The morainic uplands 
were covered with a typical climax beech-maple- hemlock forest, 
which has been sufficiently described elsewhere (10, 12). In some 
places this is almost untouched, and in at least two places, near 
Lake Michigan on the west and south of Long and Rush Lakes, 
the tension zone between it and the sand ridge vegetation is in prac- 
tically its original condition. In the first locality this zone is about 
a quarter of a mile wide, and its elements mingle with those of the 
sand ridge formation. On the south it descends the steep Algon- 
quin terrace to the shores of Long Lake, and merges with the cedar 
forest between Long and Rush Lakes, and south and east of Platte 
and Little Platte Lakes (fig. 7). North of Little Platte it originally 
stopped on the crest of the steep bluff which borders the Otter 
Creek valley, and the bluff was occupied by a xerophytic conifer 
association, of which only a few patches now remain, 
Development of communities 
As already stated, the purpose of genetic synecology is to indi- 
cate the successional relationships of the communities of a region, 
and the place of each in a developmental series. In the present 
study there is no rock substratum present, and only a very restricted 
amount of clay or gravel, so that the communities found are largely 
confined to the psammosere and the hydrosere. Secondary suc- 
cessions are present, both in burned areas and to a limited degree 
in clearings, but in the present paper the chief concern will be to 
trace the stages of the original succession (prisere). With one or 
two minor exceptions the influence of climatic and physiographic 
factors is so slight as to be negligible, and the region is so young 
geologically that there seems to be no necessity for the consideration 
of paleoecological relationships. 
SAND SUCCESSION (PSAMMOSERE) 
PIONEER STAGES.—X erarch.—The pioneer stages of this succes- 
sion are confined to the strip of shifting sand along the lake. The 
initial vegetation includes Ammophila arenaria as the absolute 
