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 : 



" In 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 



