^52 
HAROLD’S DISCUSSIONS. 
The oak is a slow and liardy grower, but in time the 
beech destroys it even on its most favorable soil. 
In ISTew Zealand a watercress grows so abundantly 
that the streams were kept open only at great expense. 
Recently willow-trees were planted on the banks; 
these have proved a successful competitor of the lusty 
cress, for they draw away its sustenance. 
In the wild uncultivated parts the forest trees are 
steadily encroaching on the weaker plants of the 
prairies. Our native weeds have little show in the 
struggle with their more thrifty cousins introduced 
from Europe, and our useful cereals, if unaided by 
man, stand no show against either. 
“Mr. Darwin,” says Wallace, “observed on some 
extensive heaths of hundreds of acres, near Farnham, 
in Surrey, a few clumps of old Scotch firs, but no 
young trees. Some portions of the heath had, how¬ 
ever, been enclosed a few years before, and these en¬ 
closures were crowded with young fir-trees, grow¬ 
ing too close together for all to live; they were not 
sown or planted, nothing having been done to the 
ground beyond enclosing it so as to keep out cattle. 
On ascertaining this, Mr. Darwin was so much sur¬ 
prised that he searched among the heather in the 
unenclosed parts, and there he found multitudes of 
little trees and seedlings which had been perpetually 
browsed down by the cattle. In one square yard, at 
a point about a hundred yards from one of the old 
clumps of firs, he counted thirty-two little trees, and 
one of them had twenty-six rings of growth, showing 
that it had for many years tried to raise its head, above 
