THE POPULATION OF AN OLD APPLE TREE 



305 



works in the flesh of the apple, its location being marked 

 by a conspicuous surface scar. The apple -maggot works also 

 in the flesh, burrowing through it in all directions, and leav- 

 ing discolored streaks from which rotting proceeds. Then 

 there are beetles, whose larvae are borers, the most injurious 

 of which work beneath the bark of young trees at the surface 

 of the ground, more or less completely girdling the trees. 

 Two or three of these burrows may kill a large tree. These 

 illustrate the appalling harm that may come from a small 

 wound in a critical place ; these cut off the tree-cro\\TL from 

 its base of supplies. 



Fig. 132. A plant bug, 



its nymph. 



and a leaf-hopper. 



These are the worst of the apple pests. Others there are 

 in plenty, that feed here and there, now and then. Plant 

 bugs and leaf -hoppers are always present in some numbers 

 among the foliage, feeding. And in an old tree, having much 

 dead wood present, there are sure to be foimd wood-destroy- 

 ing beetles of most of the sorts mentioned in Study 24. 

 And each and every one of these species has its enemies 

 and its train of parasites. 



The apple tree is useful to us, but it is necessary to many 

 lesser creatures, for it fiunishes all their living. It is the 

 center of a considerable population, the inter-relations of 

 which are of infinite complexity. There is no living thing 

 that either lives or dies unto itself alone. 



