14 THE ROYAL SOCIETY OF CANADA 



with reference to "sick soils," and in addition such sanitary measures 

 as the disposal of debris that harbor fungus or bacterial disease germs, 

 in fact it includes the control of all conditions that favor normal 

 optimum plant development. Intelligent attention to nutrition and 

 sanitation, that is to those factors that make for strong, vigorous, 

 highly product?ive growth, goes a long way towards the maintenance of 

 healthy crops. It is just here that the services of the plant physiolo- 

 gist can be of inestimable value. 



(c) Of all the methods of control those of eradication are perhaps 

 the most difficult of application. We are trying them on the wheat 

 rust problem by pulling out the barberry and the mahonia — perhaps 

 a hopeless undertaking in the eastern part of America ; we made a feeble 

 and unsuccessful attempt on the blister rust of the pine ; but we appar- 

 ently were successful in Canada in the case of the European potato 

 canker. While in most instances complete eradication is too much to 

 expect, yet the degree of success attainable may fully justify the meas- 

 ures employed. Such appears to be true with respect to potato 

 mosaic and leaf roll, as I have already indicated in an earlier part of this 

 paper. One of the main problems encountered here, as in other 

 instances after complete or partial eradication, has been the main- 

 tenance of healthy seed, but even this difficulty is being overcome by 

 inspection and seed certification. 



In dealing with eradication problems let me refer to disease 

 surveys though they are of importance in various other connections. 

 An organized disease survey such as has been launched for the first 

 time in America, an outgrowth of the activities of the War Emergency 

 Board of American Plant Pathologists, promises to be a valuable aid 

 in locating new and especially newly-imported diseases before they 

 have spread so far as to make eradication difficult or impossible, and 

 on this and many other grounds such surveys are worthy of support. 



{d) The problems of disease exclusion are manifold and often intri- 

 cate and perplexing. One of the most important and feasible means 

 of exclusion lies in the selection of sound seed. Though some diseases 

 can be avoided by seed treatment, yet that is not true of several of the 

 most serious; the safest and best rule is always healthy seed. The 

 most perplexing problems have to do with the exclusion of diseases 

 from other countries — the problems of international phytopathology — 

 and the exclusion of diseases from other provinces or states, or even 

 from other localities within the same state. Here we are confronted 

 with legislative problems, with inspection problems — too often left 

 to entomologists who have little or no knowledge of plant diseases — 

 with quarantine problems, with ignorance of the actual or potential 



