66 STRUGGLE FOR EXISTENCE. 



where the conditions of its life were so favorable that many 

 could exist together, and thus save the species from utter 

 destruction. I should add that the good efEects of inter- 

 crossing, and the ill efEects of close interbreeding, no 

 doubt come into play in many of these cases; but i will not 

 here enlarge on this subject. 



COMPLEX EBLATIONS OF ALL ANIMALS AND PLANTS TO 

 EACH OTHER IN THE STBUGGLB FOR EXISTENCE. 



Many cases are on record showing how complex and unex- 

 pected are the checks and relations between organic beings, 

 which have to struggle together in the same country. I 

 will give only a single instance, which, though a simple 

 one, intea-ested me. 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 inclosed 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 pass- 

 ing 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) fiourished 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 seen 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 inclosed, so that cattle could not enter. 

 But how important an element inclosure is, I plainly saw 

 near Farnham, in Surrey. Here there are extensive heaths, 

 with a few clumps of old Scotch firs on the distant hill- 

 tops: within the last ten years large spaces have been 

 inclosed, and self-sown firs are now springing up in multi- 

 -tudes, so close together that all cannot live. When I 

 ascertained that these young trees had not been sown or 

 planted I w:is so much surprised at their numbers that I 



