142 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. 
VOL. 2 NO. 3. 
found near the southeastern corner of the county, within a few 
rods of the shore. Here it covers an area of several acres on a 
knoll composed of large crystalline boulders with but scanty soil 
between. The dominant shrubs are old and tall, and while they 
stand close together, their thin crowns shade the ground but light- 
ly, so that the floor shows the typical heath vegetation of Poa, 
Antcnuaria, etc. The most interesting fact is that among the 
sumach grow numerous young witch hazels. These are as yet 
over-topped bv the sumach almost everywhere, but are growing 
vigorously. It will be interesting to see whether the witch hazel, 
by reason of greater shade tolerance, will not gradually drive out 
the sumach and with it the xerophilous floor vegetation, so as in 
the end to convert this typically xerophytic thicket into a meso- 
phytic one. 
Small thickets are occasionally met with, sometimes covering 
several square rods, which are composed exclusively of a single 
species. One of the small trees or shrubs which has a tendency to 
form pure growths is the crab apple. Such crab apple thickets 
within which not a single foreign shrub is seen, though many 
other species may occur in the neighborhood, are found in various 
places along the bluffs of the Menomonee Valley. Another kind 
of pure growth is sometimes formed by the aspens (both Populus 
trenuiloidcs and grandidentata) . These species (although not un- 
common and growing more frequent if the large proportion of 
young plants is evidence thereof) do not form a conspicuous 
feature of the plant life of the Milwaukee region. Where they 
do occur they usually assume their normal tree form, while farther 
inland, notably along the Kettle Range in Waukesha County, brush 
woods composed of aspen shrubs are numerous. Here and there, 
however, in our territory thickets of aspen are found. In these 
cases they consist of shoots springing from root suckers that pro- 
ceed in more or less circular form from the mother plant in the 
middle. The latter can usually be distinguished easily by its 
somewhat greater height and trunk diameter, although it never 
grows to be a tall tree. 
Very puzzling is the existence of thickets in one or two places, 
composed prevalently of Ptelea trifoliata. This shrub is found 
exclusively in the Menomonee Valley and the adjacent bluffs. 
Here it is exceedingly common, occupying stations of great va- 
riety, from those decidedly dry to those which are almost swampy. 
Nowhere else in this region has it ever been found, to 
my knowledge, but within its province it propagates freely. It 
bears seed abundantly year after year, and its seedlings are found 
of every age. Usually it mingles freely with other species, but 
occasionally it forms almost pure growths of small extent. 
