76 PROTECTION OF PLANTS — 1923-24 



we cannot permit even now more than a very low percentage, viz. 2%, of leaf 

 roll and mosaic and 3% of wilt and black leg. 



There is, however, one very important point that we should consider, — 

 though a disease may be easy or difficult to control by seed treatment, there is 

 an important group of diseases which can not be recognized in or on the seed 

 itself, at any rate, hardly 4n a quantitative sense such as would be possible to a 

 more satisfactory extent in the field. No manner of simple analysis of seed 

 would reveal the loose smuts of barlej' or wheat, the club roots of turnips and a 

 good manj^ more. 



Hence, as far as a good many diseases are concerned, we should start in the 

 field. 



The first point to decide is which of the diseases affecting plants are really 

 carried by the seed? Is the Cercospora spot of mangolds carried by the seed? 

 The Phoma disease? Is it possible to safely distinguish the discolouration of 

 the germ end of grain due to frost from various bacterial troubles? 



It seems to me that the question of disease dissemination by means of seeds 

 is an extremely important matter, to which it would appear that sufficient atten- 

 tion has not been given. I feel that this is largely due to the fact that accm'ate 

 knowledge is lacking on the method by which seeds become infected and carry 

 the diseases. The purpose of my remarks is principally to call the attention 

 of plant pathologists to this matter and to encourage research along this line. I 

 have in my mind to suggest the preparation of monographic studies; possibly 

 this might be accomplished by post graduate workers, among other problems. 



Far too little is known of the pathogenic organisms carried by the seed, 

 and still less of the role of other organisms so persistently found on almost all 

 seeds. I need only refer to the importance of the presence of the nitrogen 

 fixing organisms on the seed of leguminous plants, as well as to the remarkable 

 achievement of eecuring such good results from what would appear to be a 

 symbiotic relation between fungi and the seeds of orchids. Surely investiga- 

 tions into these phases would seem to be warranted, and remarkably useful infor 

 mation may result from such studies. 



There is certainly every need for a study of the pathogens, and there is 

 promise enough f-'om an inquiry into the relationship of bacteria and fungi to 

 the seeds and growth of higher plants. 



There is another aspect of this matter to which reference should be made. 

 In the beginning I referred to the information which I have on the question of 

 refusing admission into Canada of seed of low germination and purity. What 

 if the presence of seed borne diseases were made a reason for the rejection of agri- 

 cultural seeds? I mean agricultural seed in a proper botanical sense. In 

 "seed" potatoes 3^ou know that such restrictions are already in existence. Indeed 

 the presence of certain diseases in potatoes debars them from entry into Canada 

 altogether — even from countries where the disease is prevalent, even though 

 the potatoes themselves may be disease free. The recent discoveries of "take 



