INTRODUCTION 3 



seems that it was very difficult for schol- 

 ars previous to the nineteenth century to 

 believe otherwise but that parasitic fungi 

 were emanations or waste products of the 

 higher plants. It was DeBary who first 

 established definitely that healthy plants 

 may be attacked and penetrated by fungi. 

 This important discovery has forever dis- 

 pelled doubt as to the parasitic nature of 

 most plant diseases. Nevertheless, the 

 economic aspect of Plant Pathology could 

 not gain much impetus as long as growers 

 were content to lose annually from five to 

 forty per cent, of their crops. It required 

 severe epidemics to arouse the attention of 

 farmers in which cases they turned to the 

 scientist for help. An instance of this is 

 the epidemic of late blight of potatoes in 

 Ireland, in 1845, which practically re- 

 sulted in famine and great hardship to the 

 people. Unfortunately, there were no 



