140 POPULAE EBEOES. 



plants. Eepeated artificial sowings of the spores 

 upon healthy plants, however, proved that thrifty 

 plants were usually fully as susceptible to the attacks 

 of fungi as feeble ones, and therefore that the feeble- 

 ness sometimes noticed in diseased plants may be 

 produced by the presence of the parasitic fungus. 

 The remedies, therefore, for plant diseases are 

 somewhat like those employed to rid our crops of 

 weeds. They are all directed either toward the ex- 

 clusion of the invisible germs or seed- like bodies 

 from which the diseases originate, to the partial or 

 complete destruction of the parasites whenever they 

 have attacked the growing plant, or to the growth 

 of the crop under conditions unfavorable to the 

 parasite. The germs of some of these parasites, 

 like certain kinds of weeds, are so universally 

 present that they nearly always infest our crops 

 when the proper conditions for their growth occur. 

 Thi=!, for example, is the case with the red rust of 

 wheat, which is found on many grasses also. The 

 fungus which produces the potato rot, on the other 

 hand is more r^are, and even in seasons and localities 

 favorable to rot, it often fails to make its appear- 

 ance unless it has previously existed in the neigh- 

 borhood. A knowledge of the habits of the fungus 

 is necessary in each case in order to intelligently 

 apply a remedy. 



