THE POPULATION OF AN OLD APPLE TREE 305 
works in the flesh of the apple, its location being marked 
by aconspicuoussurface 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-crown from 
its base of supplies. 
Fic. 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 found 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 furnishes 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. ; 
