128 PLANTS AND ANIMALS. [cHaP. 
young trees had not been sown or planted, I was so 
much surprised at their numbers that I went to seve- 
ral points of view, whence I could examine hundreds 
of acres of the unenclosed heath, and literally I could 
not see a single Scotch Fir, except the old planted 
clumps. But on looking closely between the stems 
of the heath, I found a multitude of seedlings and 
little trees which had been perpetually browsed down 
by the cattle. In one square yard, at a point some 
hundred yards distant from one of the old clumps, I 
counted thirty-two little trees; and one of them, with 
twenty-six rings of growth, had, during many years, 
tried to raise its head above the stems of the heath, 
and had failed. No wonder that, as soon as the land 
was enclosed, it became thickly clothed with vigor- 
ously growing young firs. Yet the heath was so 
extremely barren and so extensive that no one would 
ever have imagined that cattle would have so closely 
and effectually searched it for food.” 
Here we have great changes following on the en- 
closure of a piece of heath-land and the planting it 
with Scotch Firs. By excluding cattle, a chance was 
given to a dozen species of plants not previously able 
to exist on the heath; the effect of this competition 
being that certain of the heath-plants were driven 
out, or existed in diminished numbers. Owing to 
the appearance of the twelve new species of plants, 
or to the more vigorous growth of some of the old 
ones—owing to the enclosure—insects were enabled 
to exist in greater numbers, and probably there was 
a largely increased number of species. An increase 
in the number and variety of insects induces the 
