DISEASES OF THE CHESTNUT AND OTHER TREES 83 



All that they show conclusively is that cutting out advance infec- 

 tions delays the progress of the disease. 



Cutting out advance infections. The bark disease does not spread 

 in a solid line, like the advance of an army, but by scattered infec- 

 tions far ahead of the main body of diseased trees. These advance 

 infections, which commonly consist of a single tree or small group 

 of trees, become centers of local infection. It seemed probable, 

 quite early in the study of this disease, that if these isolated trees 

 which are infected in advance could be located at an early stage and 

 destroyed, the spread of the disease from that particular source of 

 infection would be stopped. Accordingly, owners of chestnut 

 timber were advised to destroy completely those trees in their 

 property which first showed signs of disease (12, 13, 20, 21). This 

 has been done by many persons, and formal experiments along this 

 line have been started in various localities (13). One of the most 

 convincing experiments has been made nearby, at the Arnold 

 Arboretum. By the destruction of five diseased trees some six 

 or more acres of mixed chestnut timber have been kept free from 

 disease. This work was begun by Mr. R. W. Curtis, with the 

 cooperation of Prof. J. F. Collins, in the fall of 1909. Obviously, 

 however, this method will not prevent reinfection from distant 

 sources; and general sanitary knowledge and common-sense 

 suggest that in order to be efficient, this method must be employed 

 by all property owners over a large area. But such unanimity 

 of action means State control, and so far only one State has under- 

 taken such control, namely Pennsylvania (13, 21). The vigorous 

 and progressive action of this State makes it certain that the method 

 of cutting out advance infections will be tested on a sufficiently 

 extensive scale to demonstrate what its practical value may be. 

 Obviously, however, if Pennsylvania is not joined in this effort 

 by New York, Maryland, West Virginia, and Ohio, the work will 

 be a great experiment, but not finally effective. Such an experi- 

 ment will, however, be worth all the money that will be spent on it, 

 whether the results are positive or negative. No merely academic 

 experiment, nor one on any smaller scale could be finally convinc- 

 ing. We may be sure that this is not the last epidemic disease to 

 appear on American forest trees, and all that we learn from this, 

 both of science and practice, will be useful later. 



