70 MASSACHUSETTS HORTICULTURAL SOCIETY 



mercial control, which from my viewpoint is the principal aim' 

 and end of forest pathology, we see that we have two very different 

 lines of attack, conditioned entirely by commercial considera- 

 tions. A shade or ornamental tree has great individual value. 

 It is under constant observation, or should be, and we can employ 

 in the prevention of disease the methods of control that have 

 been evolved with such remarkable success in the control of or- 

 chard-tree diseases. In other words, we can spray, we can adopt 

 elaborate systems of pruning and wood surgery, we can follow such 

 quarantine methods as are now used in the control of pear blight 

 and other diseases in the Pacific States (3, 4). Along these lines 

 forest pathology may be expected to evolve together with pathol- 

 ogy of fruit trees and general refinements of the practice of hor- 

 ticulture. 



When we consider diseases of the forest, however, commercial 

 conditions are quite different. It is not possible to give the indi- 

 vidual tree any considerable attention. We must consider the 

 forest en masse. This being the case, it is apparent that there 

 is indicated for forest pathology a line of evolution quite dis- 

 tinct from that which characterizes the applications of pathology 

 in horticultural practice; and for the present I may say that this 

 development will be along the line of what a physician would call 

 " preventive medicine," as is the case in animal or human disease 

 when we are considering the species en masse. Unquestionably 

 the prevention of disease, rather than the cure, is the important 

 thing in any branch of plant pathology. The elaborate treatment 

 of hollow trees, constituting a part of what is at present known 

 as tree surgery and which has been built up on a wholly empirical 

 basis, must give way in a few years to a more sane and simple pre- 

 ventive horticultural practice. The time to treat sap-rot or 

 heart-rot in a tree is not after the heartwood or sapwood is rotted 

 and the tree has become hollow, but years before, when the bark 

 has just been torn off, perhaps by the teeth of a horse, and two 

 or three square inches of wood are exposed. It is the man who 

 goes over his young shade trees at least once a year with his dish 

 of coal-tar who at the end of twenty or fifty years will have trees 

 that require no heavy bill for tree surgery. 



So far as this country is concerned, forest pathology is the 



