VIII.] PLANTS AND ANIMALS. 127 
enclosure of a piece of land to exclude the cattle 
from it induces great change: here is an instance 
narrated by Mr. Darwin :— 
“Tn Staffordshire, on the estate of a relation, where 
I had ample means of investigation, there was a large 
and extremely barren heath, which had never been 
touched by the hand of man; but several hundred 
acres, of exactly the same nature, had been enclosed 
twenty-five years previously, and planted with Scotch 
Fir. The change in the native vegetation of the 
planted part of the heath was most remarkable, more 
than is generally seen in passing from one quite dis- 
tinct soil to another ; not only the proportional num- 
bers of the heath-plants were wholly changed, but 
twelve species of plants (not counting grasses and 
carices) flourished in the plantations, which could not 
be found on the heath. The effect on the insects 
must have been still greater, for six insectivorous 
birds were very common in the plantations, which 
were not to be found on the heath; and the heath 
was frequented by two or three distinct insectivorous 
birds. Here we see how potent has been the effect 
of the introduction of a single tree, nothing whatever 
else having been done, with the exception of the land 
having been enclosed, so that cattle could not.-enter, 
But how important an element enclosure is, I plainly 
saw near Farnham,in Surrey. Here there are ex- 
tensive heaths, with a few clumps of old Scotch Firs 
on the distant hill-tops; within the last ten years 
large spaces have been enclosed, and self-sown firs 
_ are now springing up in multitudes, so close together 
that all cannot live. When I ascertained that these 
