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SECTION K.—BOTANY. 
PHYSIOLOGICAL ASPECTS OF 
PARASITISM. 
ADDRESS BY 
PROFESSOR V. H. BLACKMAN, Sc.D., F.R.S., 
PRESIDENT OF THE SECTION. 
Tue President of the Association will have expressed the satisfaction 
which all the Sections feel in meeting for the fourth time in the history of 
the Association in the great Dominion of Canada. To Section K the almost 
overwhelming size of the country and the great, diversity of vegetation, 
both natural and artificial, must have an especial appeal. 
Last year the President of Section K had to deplore the loss of three 
prominent botanists. I am less unfortunate in that our loss this year is 
far lighter. We have, however, to regret the death of Thomas Frederick 
Cheeseman, a distinguished worker in systematic botany who devoted 
himself to the study of the flora of New Zealand. 
In deciding on the subject of a Presidential Address, the vastness of 
Canada’s agricultural and sylvicultural interests can hardly be overlooked, 
even in a section the interests of whose members are in the main those of 
pure botany. It appeared to me appropriate that if possible some aspect 
of pure botany should be chosen which would have at least implications 
in applied botany. The subject of disease is, of course, one of great 
moment wherever plants are massed together in artificial cultivation. 
Some aspect, therefore, of plant pathology seemed a fit subject for an 
address on such an occasion, since in it we have a branch of botany securely 
based on scientific interest and firmly buttressed by economic importance. 
Some consideration of disease in plants seemed peculiarly apposite also 
when it is recalled that at the last meeting of the British Association at 
Toronto, in 1897, the President of this Section was Professor Marshall 
Ward, the first English plant pathologist of the modern school. The value 
of his contributions to our knowledge of disease in plants is recognised by 
all; that he should have been cut off in his prime, British botanists will 
long deplore. 
It is significant of the growth of botany in all its branches that Marshall 
Ward set himself as his presidential task a wide survey of the fields of 
mycology, parasitism, and fermentation. Needless to say, the task that 
any President of Section K can at the present time essay must be one of 
much smaller compass. 
Tn the field of plant pathology which has been so assiduously cultivated 
of late years, attention has been mainly focussed on the study of the life- 
history and mode of infection of fungal and bacterial parasites, and on 
_ the methods of controlling infection. The relationship of host and parasite 
