52 American Method of Developing Agriculture.[april, 



would in many cases be impossible, and the depredations 

 would be far more continuous and complete. These natural 

 factors consist of parasitic and predatory insects, diseases of 

 insects, birds, adverse climatic conditions, &c, and while 

 these factors exert a powerful influence in preventing a still 

 more extensive waste of forest resources, it has been 

 repeatedly demonstrated that they cannot be depended on 

 to prevent widespread devastations, or to protect the best trees 

 or the best species. Under normal conditions the tendency 

 is towards the preservation of a balance between the warring 

 factors, but the injurious insects frequently gain the 

 ascendancy, and may retain it for two, three, or even ten 

 years before the balance is again adjusted through the 

 influence of the natural enemies or a diminished food supply. 



Dr. Hopkins is of opinion that it is better to aim at the 

 artificial reduction of the insects than to attempt to introduce 

 artificially the natural enemies of the injurious insects. 



Among these natural enemies are internal or external 

 parasites, or predatory insects, which feed on the young or 

 adult pests, parasitic fungi, and bacteria. The latter some- 

 times cause epidemics among injurious insects, and often 

 exert a powerful influence in controlling extensive out- 

 breaks. "Indeed, the greatest service rendered by this 

 class of natural enemies is in the frequent sudden appearance 

 of an epidemic which kills off a destructive species of insect 

 after the latter has increased to such numbers and extended 

 its depredations over such vast areas as to be far beyond the 

 control of man or his insect and bird allies. Future investi- 

 gations may possibly enable such parasitic diseases to be 

 utilized artificially to prevent threatened invasions of 

 defoliating insects." 



Great efforts are made by the agricultural colleges in the 

 United States to attract and interest farmers in their work. 



One method, which seems to be 

 An American increasingly popular, is to bring 

 Method of Developing instruction to the farmer's door by the 

 Agriculture. use 0 f a special train, from which 

 lectures are given at wayside stations. 

 An instance of the use of a train in this way was mentioned 



