No. 4.] PLANT DISEASES. 43 



sists the invasion of the fungus, as compared with the Early- 

 Rose ; but as yet we do not know what it is. Tliere may 

 also be a difference in the flesh of the apple, and in addition 

 there may be a difference in the skin or peel. There is some 

 reason to believe that red potatoes and rough-skinned pota- 

 toes are not so liable to disease as smooth, white-skinned 

 varieties. It may be the russet apple similarly escapes the 

 scab because of possessing a more resistant peel than the 

 Fameuse ; but I think there is something more than that, — 

 some more subtle difference, resident in the living tissues of 

 the flesh of the fruit. 



Mr. Miller. Would you agree with Professor Stone of 

 Amherst, when he says that the resistance of the apple to 

 disease depends in a large measure on the physical vigor and 

 constitution of the tree ? Would that be a rule to follow ? 



Professor Jones. That is one of the important funda- 

 mental questions. I think there is no universal rule, but 

 that it depends, in some measure at least, on the disease. 

 Take the brown spot on the Baldwin, for example ; I would 

 say, from all the evidence I can get, that the ranker the 

 growth of the Baldwin the more liable it is to spot. We all 

 know that the more rapidly growing pears are more liable to 

 blight ; but we ought not to sa}^ that rapidity of growth is a 

 measure of physical vigor, — such growth may rather be an 

 index of lack of balance. Certainly it holds, as a general 

 principle, that we should aim to keep our plants in as perfect 

 physical vigor as we can ; and that, if they are in perfect 

 balance, they will, as a rule, resist diseases better. But the 

 above illustrations show that this rule is not easy to interpret 

 or apply\ 



Mr. Miller. How do you explain the brown spot dis- 

 ease of the Baldwin ? 



Professor Jones. It is probably due to a physiological 

 disturbance of water content of the apple. It is not due to 

 a germ or insect, any more than is the internal brown spot 

 on the potato. 



Mr. Miller. How general is that trouble in Vermont? 



Professor Jones. Very general some years, and other 

 years we don't see very much of it. It isn't a trouble that 



