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 

 olies 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 



