PREVENTIVES OF FUNGOUS DISEASES 265 



lies in the selection of varieties or strains of varieties that 

 are able^o resist the attacks of the parasite. In the case 

 of the grain rusts as well as of many other diseases, this 

 seems to be the only practical way of preventing injury. 

 It is of the greatest importance that disease-resisting sorts 

 be planted of all crops in which there is a variation in this 

 ability. Crop growers should always be on the alert to dis- 

 cover individual plants that are able to resist the parasites. 

 One may thus develop a strain of greatest value. 



Some years ago an asparagus field in one of the central 

 Western states was struck by the asparagus rust. In the 

 great area of reddened plants, only one stood out green and 

 flourishing. Through some peculiarity of its life substance 

 it was able to resist the attacks of the fungus. The owner 

 had the good sense to see that this plant might be made 

 the parent of a resisting race. So he saved the seed, 

 selected the most resistant plants that grew from them, and 

 in a few years was able to introduce to the trade a valuable 

 variety. 



Similar progress has been made in the selection of vari- 

 eties of cotton able to withstand the dreaded wilt disease 

 for which no remedy is known. 



The selection of disease-resistant plants and the breeding 

 of new varieties from them is now occupying the attention 

 of many painstaking men. Much progress has already 

 been made, and we may soon expect great benefit from their 

 labors. 



Another important method of preventing the growth of the 

 parasite upon its host is so to isolate the crop that the fun- 

 gus may not reach it. In the case of many diseases, the 

 spores of which are carried far and wide through the air, 

 this is not practicable. Many of the rusts, for example, 

 travel great distances on the wind, and thus reach crops 



