VII.] LESS STRUGGLE UNDER CULTIVATION. 187 



from tree to tree." These remarks will enable us to 

 understand, in part, the wonderful spread of the apple - 

 scab and leaf -blights in recent years. We, as horti- 

 culturists, are every year planting new invitations to 

 insect and fungous attacks. If we take this extra risk, 

 we must certainly prepare ourselves to meet it. Our 

 fathers' weapons can not avail against the horde of 

 invaders which we are inviting to our doors. They are 

 coming up out of the woods and the swamps and the 

 bare fields to regale themselves at the banquet which 

 we have spread. 



4. CulUvation affords places of less struggle than 

 organisms are forced to occupy under normal condi- 

 tions. Man disturbs the equilibrium or removes the 

 pressure in some direction, and a multitude is waiting 

 to spring into the void. The great potato fields not 

 only provided food, but there were few other insects to 

 dispute the possession of them ; the Colorado solanum 

 beetle saw his opportunity, and improved it. He has 

 been a successful bug. This release of the natural 

 tension, which cultivation affords, is to my mind the 

 most potent factor in the increase of our little foes. 

 Dr. Lintner declares that "nowhere else are insect 

 injuries so serious as in the United States," and he 

 attributes the fact to three causes, — the importation of 

 injurious insects, the increased destructiveness of intro- 

 duced insects, and the large areas devoted to special 

 crops. The last factor we have already discussed. It 

 is not strange that, with all the commerce with foreign 

 countries, various insects and fungi and plants should 

 be introduced, but it does seem strange that the intro- 

 duced species should become so seriously noxious, for 

 not only do many of our serious insect and fungous 



