214 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VoL. II. 



Wet subsoil— Mdiv also produce unhealthy trees, but in this as in all 

 the above conditions the fruit will diagnose the condition. 



Cause. — This portion of the work will perhaps be the nnost interesting, 

 for we are aware that until the cause of a disease is discovered, and the 

 affection placed in its proper category, proper methods of dealing with 

 the disease cannot be instituted. It has been my object since beginning 

 these investigations to find, if possible, a probable cause of yellows in 

 the form of a micro-organism and to isolate it from the diseased trees. 

 Guided by the work of Prof. Burrill, of Champaign, 111., who has isolated 

 a bacillus from the affected trees, I proceeded in the same lines adopted 

 by him. 



To be sure there will be many who ^till maintain that soil exhaustion, 

 etc., etc , will produce the disease, but from observations of others and 

 the few which I have made myself, I have come to the conclusion that it 

 is a disease which is due to a bacillus and undoubtedly contagious or 

 infectious in character. Soil exhaustion may play a part, in that it will 

 leave a tree more liable to infection than a perfectly healthy one, but 

 aside from that I am of the opinion that it constitutes no part whatever 

 in the disease. 



There seems much variance of opinion as to whether a tree planted in 

 the place of the one which has been removed will contract the disease, 

 and it cannot be stated with any definiteness which is the correct opinion. 

 More careful inquiry will have to be made before it can be answered. 



Then again, considering that the affected tree does not generally 

 infect those in its vicinity, but ones quite removed from it, spreading in 

 this irregular manner throughout the whole orchard, and in combina- 

 tion with this the fact of the disease first showing itself in the fruit, it 

 appears to me a likely hypothesis that the flower of a diseased tree 

 contains the germ in an active state, and that it is conveyed thence to 

 other trees by bees or the wind, thus also explaining how it spreads 

 in the above described erratic manner. This to me seems the most 

 feasible proposition for the spread of the disease, but of this we shall 

 hope to be able to speak with more certainty at some future time, 



I shall now proceed to detail the results of the work. During the 

 past summer a {q\w trips were made to Niagara-on-the-Lake, and with 

 ordinary bacteriological precautions, inoculations were made into tubes of 

 agar-agar from the cambium layer of the bark. Many of these tubes 

 developed nothing, but in others some results were obtained, and so far 

 I have found three distinctive forms present in the diseased trees, which 

 forms are bacilli, and will be respectively styled A. B. and C. 



