Chap. III.] STRUGGLE FOR EXISTENCE. 87 



is abounding in individuals, even on the extreme verge 

 of their range. For in such cases, we may believe, 

 that a plant could exist only where the conditions of 

 its life were so favourable that many could exist 

 together, and thus save the species from utter 

 destruction. I should add that the good effects of 

 intercrossing, and the ill effects of close interbreeding, 

 no doubt come into play in many of these cases ; but I 

 will not here enlarge on this subject. 



Complex Relations of all Animals and Plants to each 

 other in the Struggle for Existence. 



Many cases are on record showing how complex and 

 unexpected are the checks and relations between 

 organic beings, which have ';o struggle together in 

 the same country. I will give only a single instance, 

 which, though a simple one, interested me. In Stafford- 

 shire, 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 different soil to another : not 

 only the proportional numbers of the heath-plants 

 were wholly changed, but twelve species of plants (not 

 counting grasses and carices) flourished in the planta- 

 tions, 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 



