344 



Mycologia 



population creates a bridge by which the casual organism may more 

 readily pass from plant to plant or from farm to farm. In these 

 two conditions, facility of transportation and congestion of crop, 

 we find, to a large degree, explanation of the fact that plant dis- 

 eases are more prevalent now than formerly. 



What is the nature of the return that plant pathology has given t 

 The achievements may be summarized briefly as falling within 

 seven great categories demonstrating the value of : protective ap- 

 plications, sprays and dusts ; excision ; seed steeps ; general sanita- 

 tion leading to diminution of infective material ; breeding for dis- 

 ease resistance; modifications of agricultural practice; quarantine 

 restrictions. Of all the categories mentioned, perhaps the least 

 dependent upon science and the most empirical is that relative to 

 disease resistance, since some of our most valuable resistant va- 

 rieties have been given to us by farmers, while many of the most 

 susceptible have been eliminated naturally. During recent years, 

 however, knowledge of Mendelism and of biologic specialization 

 has added a very important, truly scientific aspect to this somewhat 

 empirical subject. 



It is to be observed that the great discovery of the parasitism 

 of the fungi and the founding of bacteriology and the development 

 of its methodology, together with the early foundations laid 

 through the years in histology, mycology, taxonomy and physi- 

 ology, have furnished the bases on which plant pathology has made 

 its advance. Aside from these there have been few, if any, great 

 fundamental contributions. The problems of disease resistance 

 and wherein it lies are obviously important. Enzymes and toxins 

 will repay much study. That group of mysterious diseases includ- 

 ing the mosaics and peach yellows holds a secret the discovery of 

 which may well be revolutionary in pathology. But since the 

 problems now before us are more intricate than those of the past 

 generation, they demand concentration, larger breadth of equip- 

 ment, longer periods of sustained research on a given problem, 

 in a word, greater specialization, and this often needs to be accom- 

 panied by cooperation of widely separated branches of science or 

 of distinct sciences. 



