FOREST PATHOLOGY IN" FOREST REGULATION. 53 



years, these cases become more and more frequent. In most cases, 

 to judge from this table, frost cracks are a strong factor for extending 

 typical decay much beyond the point of entrance of the fungus. By 

 splitting the bole for a considerable length they allow air to enter the 

 wood, which evidently stimulates the growth of the fungus. 



In noting the cases of decay traced to the wounds or openings 

 through which the fungus found its entrance, it is seen that two and 

 even more cases of decay (cull cases) may be found on the same tree, 

 bat each case is counted separately. Where decay is traced to a com- 

 bination of two factors, each factor is shown separately. The means 

 of entrance of the fungus causing decay are thus shown to be as fol- 

 lows: Fire, 48; frost, 25; lightning, 23; other causes (including knots, 

 girdling, etc.), 13; total, 109. 



These 109 wounds (including knots, etc.) led to 97 cull cases. Out 

 of 109, only 13 were other than wounds from fire, frost, and lightning, 

 and 11 of the 109 cases of decay were the effect of a combination of 

 two of the causes named. Fire has by far the greater share; frost and 

 lightning are second, but the preponderance of fire and frost over 

 lightning is greater than would appear, since they are far more serious 

 with respect to causing decay. If ratings are given, more or less 

 arbitrarily, but yet in keeping with our field observations, to the var- 

 ious causes of wounds in the order of their importance with relation 

 to damaging decay in white fir, taking injury from lightning (the 

 least consequential) as the unit, we have: Fire, 3; frost, 4; lightning, 

 1; other causes (including knots, girdling, etc.), 3. Then, multiply- 

 ing the figures for means of entrance by these relative ratings we have: 

 Fire, 144; frost, 100; lightning, 23; other causes, 39. These figures 

 express the following facts: (1) Fire injury is not only numerically the 

 strongest, but also commonly leads to considerable cull; (2) frost dam- 

 age is less frequent (above all, less ubiquitous) than fire damage, 

 because it appears only in typical frost belts or frost holes, but it car- 

 ries decay over a much greater length of the bole; (3) lightning injury 

 is fairly common, is also restricted to certain belts, and leads more 

 often to superficial rot; (4) other factors are of importance as causes 

 of damaging decay, but they are comparatively rare. 



CONCLUSIONS AND OUTLOOK. 



The interpretation of the results of this study of the white fir from 

 a practical point of view can not leave out of consideration the fact 

 that the basis for all computations and tables is a comparatively small 

 one and that the actual figures and many of the principles derived 

 therefrom have more the value of strong indications for local appli- 

 cation than the force of general laws. Still quite a number of the con- 

 siderations will be directly applicable, at least in all similar types, 

 some throughout the range of white fir. The writer would emphasize 

 again that the aim of the present study is not to lay down laws, but 



