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PRESIDENTIAL ADDRESS 



or other fungi. For instance it is estimated that 10 per cent of the 

 apple crop and one-half of the sweet potato crop are lost after harvest- 

 ing, chiefly from fungous diseases — a matter of direct concern to 

 producers, railroad and express companies and handlers, not to 

 mention consumers, who in the end must pay the piper. Attention 

 has been given to this subject by plant pathologists and control 

 measures would, if applied, effect the saving of a considerable part of 

 this deplorable waste. But many problems, not the least of which is 

 Education, are still unsolved. 



(3) Turning from the parasitic diseases we find another group of 

 diseases of unknown origin to which the name "physiological" or non- 

 parasitic is applied. Not only are some of these diseases prevalent 

 and highly destructive but they present some of the most attractive 

 problems in the whole field of plant pathology. I need but refer to 

 the so-called mosaic diseases of tobacco, potatoes, beans, etc., spike 

 disease of sandal, leaf roll of potatoes and yellows of peach and rasp- 

 berries. The solution of the problems of etiology and of environment 

 in this group call for the most refined methods employed in studies 

 on parasitology, and special training in physiology and bio-chemistry. 

 That there is hope of the formulation of successful preventive measures 

 has apparently been fully demonstrated by the Canadian Department 

 of Agriculture judging from the satisfactory results of investigations 

 on moasic and leaf roll of potatoes. The following tables illustrate 

 the ecomomic importance of these two diseases in Canada:* 



Mosaic of Potatoes 



The following experimental data show losses from mosaic of 

 potatoes (as reported from various districts in Canada). 



These figures are quite in accord with what appeared to be the 

 common opinion, viz., that mosaiced plants give on the average only 

 about half the yield of healthy ones. 



* Emergency Board — American Plant Pathologists. Report of the Conference on 

 Diseases of Potatoes and Seed Certification, Buffalo, Aug. 16-17, 1918. 



