16 TRANSACTIONS OF THE [Sess. lxxvi. 



be of some use, I think. We have Local Secretaries and 

 members almost all over the country, and no doubt many 

 would be quite willing to make systematic observations on 

 the occurrence, spread, and severity of plant diseases in 

 the forest, field, and garden of their own particular area. 

 Doubtful cases of any disease, the cause of which was not 

 evident to the local representative, might be sent in to 

 headquarters, where a Special Committee might investigate 

 and report. The reports and records of the Local Agents 

 and those of the Central Committee would in time become 

 not only of scientific interest but of great practical utility. 



The making and recording of these observations may 

 seem all very simple and such as anyone might be able to 

 make, but I do not propose for one moment that such 

 records should contain a mere list of parasitic fungi found 

 from year to year ; such lists alone would have very little 

 scientific or practical value. 



These investigations could only be carried out by 

 botanists. They would have to be of the nature of an 

 recological study of the disease. Such factors as the 

 influence of the soil, the climatic influence, the local 

 method of cultivation, the nature of the attack — slight or 

 severe — the presence of other plants, in fact all the con- 

 ditions in the physical and organic environment which 

 influence the relationship of host and parasite would be 

 noted and recorded. It is only by such means that we 

 can gain any clear and definite knowledge of the con- 

 ditions in nature which influence the increase or decrease 

 of disease. It is only when we are in possession of such 

 records that prophylactic measures can be evolved, and 

 plant hygiene placed upon a sound scientific basis. 



The complete study of a plant disease may be presented 

 as follows : — First, we should learn to diagnose the disease 

 from its outward visible effect on the plant. This may be 

 called the symptomatology of the disease. Then comes 

 the study of the aetiology, or the investigation of the 

 cause. Then, after the cause is known, we are in a posi- 

 tion to find out the cure and future prevention, namely, 

 the therapeutics and prophylaxis. The first and last of 

 these, namely, the diagnosis and prophylaxis, are the most 

 important from the economic standpoint. 



