The Effect upon the Host-Plant. 231 



sites is, as a rule, deserving of his loss, for means of destroying 

 the pests are at his command. It is largely the grower's fault if 

 his apples are scabby, if his grapes are mildewed, and if his 

 potatoes rot in the field. Spraying is no longer an experiment, 

 it is a necessity; and those who recognize this fact are the 

 ones who are reaping the rewards. 



III. UPON THE HOST-PLANT. 



Insecticides and fungicides are applied solely for their action 

 upon the organisms it is desired to destroy, since in other respects 

 most of the preparations possess no value. If properly applied 

 they are harmless to the plants, and should not in any way 

 interfere with their proper growth nor with the sale of the 

 products. When some of the mineral preparations, however, 

 are too freely used late in the season, the appearance of the 

 crop may reduce to a considerable extent its market value, 

 although the product may be still as wholesome as if untreated. 



Fears have also been entertained that some substances are 

 dangerous even when not visible, on account of their effect 

 upon the crop, which was supposed to be poisoned. This sub- 

 ject was well agitated when Paris green and London purple 

 began to be commonly used in the destruction of the potato 

 beetle. Many analyses were made, but no arsenic could be 

 found, either in the tubers or in the parts above ground, and 

 soon all fear of arsenical poisoning disappeared, and potatoes 

 treated with the arsenites were used without question. Another 

 equally groundless objection was raised in England regarding 

 American apples which had been sprayed for the canker-worm 

 or codlin-moth. It was said that the bloom found on American 

 apples consisted largely of the arsenic which had been applied 

 to the trees to destroy insects, and that such apples were unfit 

 for use. These reports have led to many chemical examina- 

 tions of sprayed fruit, and only in rare cases has even a trace of 

 arsenic been found. It is only when very late applications are 

 made, such as are utterly useless, that any of the poison is found 

 upon the fruit, and then the quantities are so minute that they 

 could in no way cause injury to the consumer. But even though 

 all the poison sprayed upon the apples in making necessary 

 treatments should remain there undisturbed, a person would be 



