JULY, 1902. BRUNCKEN — STUDIES I.\ PLANT DISTKIBUTIOX. 139 
the greater portion of the surface. With its dense tangle of fili- 
form roots, the dense sward of Poa makes it exceedingly difficult 
for other species to compete. About the only successful rivals are 
a number of minute mosses, and Antcnnaria plantaginifolia. The 
latter is almost always present, forming little groups and patches 
in the sward. Where there are other species in the grass carpet, 
it will invariably be found that they grow in places where from 
one cause or the other the sward has been broken or prevented 
from forming. Thus they will grow from under the. edge of a 
boulder or cobble stone ; out of a hole made by an animal ; or a 
place where the surface water has laid the ground bare. Among 
the species conspicuous in such spots are Fragaria virginiana; 
Viola sororia; Potcntilla Canadensis ; here and there Hedeoina 
pulegioides ; further Monarda Ustulosa; Verhasciim thapsiis. It 
will be noticed that many of these xerophytic heath plants have 
creeping root stocks, runners and stolons, which fit them to com- 
pete with the dense grass better than propagation by seeds could 
do. Of late years the common ragweed invades these dry hillside 
pastures in great numbers. It colonizes especially places where 
sod has been removed, and thence spreads to every bare spot it 
can reach. Occasionally places are found where one of these 
herbs, most often Potcntilla, has managed to drive out the grass 
from considerable areas, and now forms an exclusive carpet many 
square feet in extent. 
In the meantime, the shrubs which started out evenly with the 
grasses have established themselves in groups here and there. It 
is especially Crataegus which has its favorite habitat on these dry 
heaths. There are in this vicinity probably some six or seven 
distinct species of this genus. But as they have never been thor- 
oughly studied taxonomically, they may simply be grouped as 
C. coccinea, C. mollis and C. punctata, wiih. their respective allies. 
They occur within the forest as well as on the heath. But as they 
need a great deal of light they are apt to assume quite eccentric 
forms in shady places. Their normal adult form is that of a 
low tree with spreading crowns, approaching the umbrella-like 
shape so common in Mimosa and other trees of tropical and sub- 
tropical savannas. In deeply-shaded woods, on the contrary, 
they shoot up high, with few and thin branches. I have seen 
hawthorn trees twenty feet high, two inches in diameter, bearing 
no branches below^ a height of ten feet above the ground, and then 
sending out but few and short ones, without the multitude of spurs 
that make the typical crown of a hawthorn so dense. 
An old hawthorn on the heath, however, usually has a sturdy 
trunk, five or six inches in diameter. Its crowm is disposed like 
a number of galleries one above the other, with distinct intervals ; 
