140 BULLETIX OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 2 NO. 3. 
the tips of the branches sweep within a few feet of the ground. 
Under its immediate shade the ground is bare of vegetation ; but 
at the edge of the bare spot there is often a ring of mesophytic or 
moderately xerophytic herbs, such as golden rod, violets, milk- 
weed, etc. The younger individuals of hawthorn are apt to suffer 
much from cattle and in their efforts to protect themselves often 
assume the grotesque shapes described elsewdiere. (i) As a re- 
sult, they remain shrubby much oftener than would be the case 
if the normal tendency of the genus to assume the tree-like form 
had its full sway. 
It is very noticeable that the shrubs and small trees scattered 
over the heath tend to grow in groups. It is rare to find a single 
shrub or young tree. The reason for this may be that single seed- 
lings are almost certain to be eaten or trampled by cattle, while 
where they occur in patches or groups, some of them at least 
have a chance of surviving. When they are a few years old, the 
young shrubs begin to protect each other. The older a group be- 
comes, the more mesophytic the conditions in their midst and for a 
few feet beyond become, especially on their north and east sides. 
Soon many mesophytic herbs, such as Podophyllum peltatum, 
Anemone nemorosa, asters, golden rod and sun flowers reappear, 
while Poa gradually dies out. More mesophytic shrubs soon make 
their reappearance. By and by the group develops into a small 
thicket, and as this spreads and joins with its neighbors, the whole 
heath may in time be converted into a thicket. While this goes on, 
young trees, especially oaks and hickories, will have found favora- 
ble lodging places among the shrubs, and the development will, 
if undisturbed, progress until the mesophytic forest has again 
taken possession of the area. 
On heaths of this description, the various species of Crataegus 
are decidedly dominant among the shrubs. The other species 
most frequently found are the hazelnut and two species of sumach, 
Rhus typhina and Rh. glabra. (2) There are, of course, a good 
many others, such as Symphoricarpus, Diervilla, Rosa, Amelan- 
chier, but they rarely give character to an area of considerable ex- 
tent. On heaths in the close vicinity of the Lake Shore, Juniperus 
alpinus is a very characteristic shrub. 
The thickets found in the neighborhood of Milwauke are not 
always, nor perhaps even commonly, developed from the Poa 
heath formation. Where the exposure of the slope from which 
the forest is removed is towards the north or east, so that the 
insolation is comparatively small, the forest litter does not disap- 
1. Bulletin Wis. Nat'l Hist. Soc, Vol. I, page 183. 
2. It is a remarkable fact that these two species hardly ever intermingle. Rh. 
glabra seems to be a little less xerophilous than its cousin. 
