Some Important Pear Diseases. 297 



the cambium, which develops each year a layer of new wood on the 

 inside and a layer of new bark on the outside, so that all the young, 

 active tissue is very closely connected. The younger inner bark, how- 

 ever, is the favorite region for the bacterial growth, containing, as 

 it does, much nutritive material. 



Sometimes the cambium is also affected. In these tissues the bac- 

 teria grow abundantly, passing gradually from cell to cell and destroy- 

 ing much of the living portion of the branch as they go, but never 

 circulating rapidly from branch to branch. The surface is reached by 

 means of the little cracks through which the gummy exudations arise. 



4. Remedies. - 



(a.) The knife and the saw. — With a disease working as this does, 

 it is very evident that there is no chance either for cure or prevention 

 by means, of spraying. The heroic treatment of the knife and saw 

 must be adopted and vigorously pursued, as has been claimed from 

 the beginning. The blackened leaves, alone, must not serve as signs 

 of the diseased area, but one must examine carefully the branches and 

 remove them six inches or more below the lowest discolorations. Often 

 before cutting, pruners slice the bark downward to see where the injury 

 ends. This should not be done; it is better to be sure that you are 

 below the infected area and run no such risk of infecting anew the 

 tissue below. The cut surfaces of larger hmbs and branches should 

 be painted for protection against wound rots. 



{b.) When to cut. — Cutting out diseased portions should be done 

 whenever the disease is evident. This may check the injuries tempo- 

 rarily; but it has been shown that much can be done in the autumn 

 to prevent the establishment of the disease the following spring. It 

 has long been known that the disease may pass the winter in the 

 branches by a slow growth in the neighborhood of late infections. 

 Thorough work of eradication should especially be performed after the 

 season of growth. Then cut out every diseased branch and bum, so 

 that in the spring, when the succulent growth begins again, there will 

 be few places in which insects may come in contact with the bacterial 

 exudations. Sometimes trees which are affected during the summer 

 and autumn show no indication of the disease the next year, and I 

 have observed this especially in the case of hawthorn and apple, but 

 it seems much more likely to pass the winter in the pear. 



