24 
BnXETI>- OF WISCOXSIX >-ArCRAL HISTORY SOCIETY. VOL. 2. XO. 1. 
end of the Lake were formerly connected by a strip along the Lake 
Shore (5). 
The signs that the maple-yellow birch-hemlock association 
was ever present in this neighborhood are not quite so convincing 
as those of the white pine association. The only direct evidence 
discovered so far is the occurrence of Betiila hitea in this neigh- 
borhood (see Bull. Wis. Natural History Soc., L page 31). But 
there is good theoretical ground for assuming such a stage in the 
histor}' of our torest. For in the regions to the Northward, the 
white pine association is normally succeeded by this or similar as- 
sociations, the development proceeding from the interior to the 
shore (6). 
The white pine association is of course typically xerophytic; 
the only other xeroph\tic forests found in our region are the 
tamarack swamps, which were formerly quite extensive but have 
now almost disappeared, principally through the direct activity of 
man. 
The result of this inquiry into the historv' of the forests of 
the Milwaukee region is the following: 
The earliest forests of which we can find any trace belongs to 
the xerophytic white pine association. It was probably succeeded 
more or less completely by a forest similar to the hardwood forests 
of Central Northern Wisconsin, in which maples, yellow birches, 
and perhaps hemlock played a leading part. Whether this group 
ever occupied the whole area not reser^-ed to the white pine asso- 
ciation, or whether in some places the pines were directly sup- 
planted by the oaks that must have invaded the territory from 
the Southwest, it is now impossible to tell. Nor is there any clear 
evidence to show what caused the birches to disappear. It is cer- 
tain that the oaks successfully conquered the whole territory* ex- 
cepting the swamp lands and river bottoms, which developed dis- 
tinct associations. What gave the oaks their temporary advantage 
over the maples and birches we do not know. After a while the 
maples, but not the birches, began to reconquer the lost ground, 
and the forests progressed towards a basswood-maple-beech cul- 
mination type, when the interference of man gave a renewed ad- 
vantage to the oaks. 
IL Cootributioos to tlie Ecology of the Genus Viola. 
The fact that a large number of plants growing in undrained 
swamps have numerous xerophytic characters is well known. 
The immediate shore of Lake Michigan, i. e. the beach, terraces, clay 
banks and ravines, have so distinct and peculiar a flora that they deserve separate 
treatment, which must be reserved to a later time. 
("6) See H. N. Whitford, Genetic Development of the Forests of Northern 
Michigan, Botanical Gazette, vol. 31; May, 1901. 
