2 THE ROYAL SOCIETY OF CANADA 



true the fructifications of fungi were often seen on the surfaces of 

 diseased plants, but they were thought to be excretions or transfor- 

 mations of the sap of the host plants, for no one had as yet distinguished 

 bacteria or fungal hyphse in diseased tissues^ — something not to be 

 wondered at when it is remembered that the cell theory itself was not 

 proposed before 1838. Evidently as long as it was not possible to 

 differentiate the general causes of disease in plants a beginning in 

 plant pathology was out of the question. 



In tracing the early history of a science it is rarely, if ever, possible 

 to designate any one man or any single event as the starting point; in 

 fact many men and many events in greater or in less degree, more or 

 less independently have shared in the inauguration of every science. 

 So it has been with the science under discussion. Yet there is one 

 name in the early history of plant pathology that stands out above all 

 others as that of a fertile investigator of fundamental principles and as 

 a marvellously fructifying influence whose potency is still felt. I 

 refer to the botanist DeBary. DeBary brought new methods to bear 

 on his subject ; his point of view was new. His methods were develop- 

 mental rather than anatomical; for with the aid of pure cultures 

 wherever possible, following the practices of Pasteur, he traced the life 

 histories of the parasites under investigation step by step from spore to 

 spore, observing closely at the same time their relationship to and 

 effects on their hosts. The result was that his researches made 

 possible for the first time the distinction between biotic and abiotic 

 causes of disease in plants; they demonstrated for the first time the 

 existence of parasitism among fungi; they revealed the way in which 

 infection takes place, and explained the phenomena of epidemics. 

 Such of his papers as those on smuts (1853), the potato blight, its 

 cause and its prevention (1861), and the heteroecism of wheat rust 

 (1863) opened up new lines of inquiry that were epoch making. But 

 even more important still he imparted to his own students and to 

 botanical students the world over a burning enthusiasm that still 

 persists, and which more than any other influence has been responsible 

 for the laying of those solid foundations of scientific fact and method 

 on which the science of plant pathology rests. 



With DeBary's name, however, we should couple that of Millardet, 

 for it was Millardet perhaps more than anyone else who first turned to 

 practical account the new discoveries on parasitism. DeBary showed 

 how to work out the etiology of a plant disease, Millardet showed how 

 to control it. This he did especially in the use of Bordeaux mixture, a 

 spray of his own compounding (1882). Millardet, who had received 

 some of his earlier training in DeBary's laboratory, was commissioned 



