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BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 2. NO. 1. 
olnut and witch hazel. In places there are thickets of Riihus, and 
Xanthoxyluni is not uncommon. The herbaceous flora is rich, 
both in species and individuals, and golden rod, sunflower and 
asters find here their favorite habitat. 
The second sub-association is characterized by the great shade 
tolerance of some of its members, and probably as a consequence 
of the deep shade prevailing in its midst, by the thick layer of 
humus found on the floor. In addition to the hard maple and 
basswood, there belong to this association the butternut, the black 
walnut (now rare), and the white ash. The underbrush is apt to 
be less dense than the preceding class, and often confined to the 
places where the canopy has been broken. It is composed largely 
of the same shrubs that are found in the preceding sulD-association, 
except that the hazelnut is not likely to be found, and that Sam- 
bucus nigra may be added. The herbaceous vegetation is apt to 
be scanty, especially in summer, when the crowns are fully leaved. 
Often the dry leaves monopolize the floor almost entirely. Among 
the herbs most often accompanying this association should be men- 
tioned Podophylhim peltatum, Viola scahr'msciila, Trillium grand- 
iflonun, and two species of Erythrofiiiuu. 
This sub-association rarely occupies large areas ; it is usually 
found in the form of islands among the surrounding sea of the 
hemi-xerophytes. Often it inhabits damp ravines, where the ac- 
cumulation of humus is assisted by washing from the sides. As 
the two associations are still in the fighting stage, neither is very 
firmly established in any particular locality. Consequentlv it is 
by no means uncommon to find individuals belonging to the one 
sub-association scattered among the other. But in those places 
where there has been no modification by human interference such 
as will be described below, this difference is quite noticeable : The 
hemi-xerophytic trees scattered among the maple-basswood sub- 
association are usually old, often veterans in a state of evident de- 
cay ; on the other hand, where maples, basswood and their associ- 
ates are found among the oaks and hickories, they are more often 
young trees. This phenomenon will throw considerable light on 
the history of these forests, and should be borne in mind for the 
discussion which will follow below. 
The hemi-hydrophytic sub-association may again be divided 
into a double group, according as it is found in the swampy de- 
pressions of the uplands or in the river bottoms. The difference 
is not so much in the species as in the way in which they are asso- 
ciated. In the upland swsimps (2) Ulmus Americana and Frax- 
(2) These swamps are tisnally fairly well drained, dry after about the first 
of July, and very distinct from the tamarack swamps. Their center is nsttplly in 
part open water, in part occupied by the swamp loving shrubs mentioned in the 
text. 
