2 The Spraying of Plants. 



sions which, from the outset, are founded upon a sound and 

 logical basis. It is fortunate that this is the case. The number 

 of the enemies of cultivated plants is either now more numerous 

 than formerly, or the attacks are much more energetic. It is 

 undoubtedly true that the maladies of cultivated plants are 

 much more widespread. This fact is mostly due to the greater 

 food supply, and to the greater ease with which most of the 

 injurious forms can pass from one part of the country to an- 

 other, because the cultivated areas lie so close together. If a 

 plant is grown to any considerable extent, it is easy for its ene- 

 mies to spread over the entire region in which it is cultivated. 

 Physical barriers are almost without value in checking this 

 spreading of disease. The ocean is only a partial exception, 

 since such close means of communication have been established 

 between all parts of the globe that this obstacle is now of little 

 avail. Some diseases have not yet been able to overpass it, but 

 as it has proved of little hindrance in so many cases, it is probable 

 that ultimately the enemies and diseases of plants will be as 

 widespread as are the plants upon which they flourish. Weedy 

 plants, insects, and possibly also fungi, are frequently more 

 destructive in a new country than in their old home. They are 

 freed from the enemies or conditions which formerly kept them 

 in check, and in some cases they are the cause of very serious dis- 

 turbance, although originally they may not have been markedly 

 destructive. 



Farmers and fruit growers cannot fence out the many forms 

 of insects and fungi which live upon their crops and which are 

 as anxious for a harvest as the grower is. It is a fight between 

 the grower and the pest, and it must be admitted that the latter 

 has generally had the best of the battle. The farmer has not 

 been properly equipped. He has often had invisible foes to 

 contend with, foes which he did not understand, and which 

 he could not assail. It frequently occurred that an entire crop 

 was ruined in a day or two, and the cause remained unseen and 

 unknown ; and even if it was visible, almost the only remedy 

 upon which the grower could rely with certainty was mere 

 force, first catching the pest and then destroying it. As this 

 could be done with profit only in rare cases, it was little better 

 than no remedy, and the general result was that the insect or 

 the fungus obtained an ample supply of nourishment, and the 



