12 fu:n'gi and fungicides 



the various kinds of summer sj^ores. With the great 

 majority of diseases these are i^roduced in countless 

 numbers, and as they are wafted hither and thither by 

 every breath of wind, are washed from leaf to leaf and 

 from leaf to root by rains, and germinate quickly in 

 their new situations, they are able to spread infection 

 with marvelous rapidity. They are also, no doubt, often 

 carried from place to place by insects and birds, adher- 

 ing to some part of their bodies, especially the feet. 



The various other kinds of sj)ores produced by the 

 fungi discussed in the following pages are also distrib- 

 uted by similar agencies. Some of the smuts, as well, 

 no doubt, as many other diseases, are often spread 

 through the field in barnyard manure ; and in cases like 

 the onion smut, the spores may be washed, with loose 

 soil, from higher to lower levels. The spores of certain 

 grain smuts appear to be able to joass from diseased to 

 healthy kernels during the process of threshing, and, 

 in some cases, the disease may be spread by means of 

 hoes and other implements used in cultivation. 



In diseases like the scab and blight, or rot of pota- 

 toes, the mycelium of the fungus is often distributed in 

 the tubers used for seed, thus being ready to infect the 

 new crop as soon as it gets well started. 



METHODS OF PREYEXTIOi^ 



There are man}' ways in which the injuries of fun- 

 gous diseases may be prevented. Among the more im- 

 portant of these are the following : 



Fertilization and Cultivation. — As a general 

 rule, — not, however, without important exceptions, — 

 plants weakened in vitality are more subject to the 

 attacks of parasitic fungi than those in vigorous growth. 

 Consequently metliods of cultivation and fertilization 

 which tend to produce rapid development and early ma- 

 turity, are to be adopted as far as practicable. 



