18 Darwinism chap. 



so as to keep out cattle. On ascertaining this, Mr. Darwin 

 was so much suri)rise(l 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 the stems of the heather and had failed. Yet 

 this heath was very extensive and very barren, and, as Mr. 

 Darwin remarks, no one would ever have imagined that cattle 

 would have so closely and so effectually searched it for food. 



In the case of animals, the competition and struggle are 

 more obvious. The vegetation of a given district can only 

 support a certain number of animals, and the different kinds 

 of plant-eaters will compete together for it. They will also 

 have insects for their competitors, and these insects will be 

 kept down by birds, which will thus assist the mammalia. 

 But there will also be carnivora destroying the herbivora ; 

 while small rodents, like the lemming and some of the ff eld- 

 mice, often destroy so much vegetation as materially to affect 

 the food of all the other groups of animals. Droughts, floods, 

 severe winters, storms and hurricanes will injure these in 

 various degrees, but no one species can be diminished in 

 numbers without the effect being felt in various complex ways 

 by all the rest. A few illustrations of this reciprocal action 

 must be given. 



Illustrative Cases of the Struggle for Life. 



Sir Charles Lyell observes that if, by the attacks of seals 

 or other marine foes, salmon are reduced in numbers, the 

 consequence will be that otters, living far inland, will be 

 deprived of food and will then destroy many young birds or 

 quadrupeds, so that the increase of a marine animal may 

 cause the destruction of many land animals hundreds of miles 

 away. Mr. Darwin carefully observed the effects produced 

 by planting a few hundred acres of Scotch fir, in Staff"ordshire, 

 on part of a very extensiv^e heath which had never been 

 cultivated. After the planted portion was about twenty-five 

 years old he observed that the change in the native vegetation 



