38 



they have now a mission to perform. They must do their part 

 in preventing too great an increase of the wood-eating beetles, and 

 so protect the young pines springing up among the ruins where the 

 forest that is to be is rising from the bones of its progenitors. 



Years roll away, and a new forest waves its branches where the 

 old trees once stood. All that remains of the old now is a great 

 trunk, forming a natural bridge across the stream. Huge and 

 moss-covered it lies, a relic of the past. Along its upper surface 

 lies a well-beaten path, traversed by the shuffling bear, the slink- 

 ing wolf or the timid deer, descendants, it may be, of the animals 

 who were sheltered by its branches in their prime. 



But, you say, what is the practical bearing of all the foregoing? 

 What the utility of the observations made? Know, then, that 

 we cannot study the relations of the creature to its environment 

 without learning something of the great plan governiug all. We 

 cannot enter upon the consideration of any of the forces which 

 regulate the increase of animal or vegetable life without being 

 brought face to face with the great laws by which the balance of 

 nature is preserved. How beautiful and yet how complex is this 

 great plan, by which each species of plant or animal fits into the 

 proper place just so long as it serves a useful purpose, then filling 

 a subordinate place, and becoming extinct when its mission on 

 this earth is ended. 



Were there no law regulating the increase of the pine, it would 

 be but a few centuries ere the whole earth would be covered with 

 pines. In such a case there could, of course, be no wood-eating 

 borers and no birds to feed upon such insects ; there could be no 

 grass-eating animals, for there would be no grass ; man himself 

 could not exist. 



Wood-eating insects are no doubt a necessity, when properly 

 held in check by the birds which feed on those insects. If a single 

 species of insect were allowed to go unchecked, it would be but a 

 few years before all the foliage upon the continent would be de- 

 stroyed. Kirkland has figured that the unchecked increase of the 

 gypsy moth (^Porthetria dispar) would in eight years destroy all 

 foliage in the United States. It is easily demonstrable that cer- 

 tain other species of insects, if unrestricted, could cause similar 

 devastation. When such insects have spread over the continent, 

 such an increase and such a devastation can only be prevented by 

 the natural enemies of those insects ; and here comes a practical 

 lesson. Man should not disturb the balance of nature. But what 

 does man do to preserve this balance of nature? Generally, 

 nothing. What does he not do to disturb it ? Man enters a new 



