218 JOURNAL OF FORESTRY 



one great forest pathologist the world has produced so far, Robert 

 Hartig, possessed this view in a remarkable degree. But Hartig's 

 field was the regulated forest of Europe, in which many of the 

 avoidable factors of loss had already been eliminated as a matter of 

 routine, and where costly control measures are often remunerative 

 on account of the intrinsically high value of the timber. In American 

 forests, with their immeasurably more complex problems, forest path- 

 ology has until recently more or less duplicated- Hartig's work as far 

 as pure description is concerned. The first necessary step, quite 

 logically, was to take an inventory of our forest diseases and to 

 study them from a purely botanical point of view. This line of work 

 is far from being complete. It is fundamental in character and its 

 value cannot 'be overrated. But it is botany, mycology, plant pathology 

 rather than forest pathology. It concentrates its interest on the aetiology 

 of a given disease, the description of the casual factor and the eflfect 

 on the individual rather than on the relative importance of the disease 

 with regard to possible loss and the bearing on the productiveness of 

 the forest, present and future. So far there exists no standard by 

 which to gauge the relative importance of a given disease; in fact, the 

 perusal of most of the contemporaneous literature on forest tree 

 diseases leaves one with the impression that all of them are more 

 or less of equal importance. Obviously that cannot be the case. There 

 are numerous diseases interesting from a botanical point of view no 

 doubt, which are negligible in the life of the tree or the forest. A line 

 must be drawn somewhere. Only a rational system of rating can 

 bring order into this chaos. 



The relative importance of a disease or of any cause of loss in 

 the forest is governed by a number of factors, of which the economic 

 value of the species affected, the character of the injury, and the 

 aggressiveness of the agency causing loss, are beyond doubt the most 

 important. The economic valuation is influenced largely by the repre- 

 sentation, range and accessibility of the species affected. Aggressive- 

 ness is judged by the virulence of the attack, the liability to spread 

 over the entire range of the species irrespective of topographical and 

 climatological influences, and the faculty of attacking other species 

 in admixture. 



To illustrate : The well-known chestnut-bark disease which has 

 swept through the East during recent years doing untold damage, 

 fairly threatens to exterminate Castanea dentata. This tree is one of 



