298 ENGLISH ESTATE FORESTRY 



is the most likely explanation of the most puzzling problem 

 of the forestry world. 



It may be stated at the outset that the life-history of 

 the fungus, as given by Hartig, Marshall Wood, Massie, and 

 others, has less connection with the practical side of the 

 problem than many suppose. For all practical purposes, the 

 life-history of the fungus may be generally accepted as 

 following the same 'course on every soil, and in all parts of 

 the country. 



The problem for solution is the cause of the great 

 difference in the degree with which one plantation, or one 

 part of a plantation is affected, as compared with another. 

 The disease is practically universal. Why, then, should 

 its virulence differ to the extent that it does ? Without 

 pretending to solve this problem off-hand, it may be worth 

 while discussing a few sides of the question which seem 

 most pertinent to it, and which may throw stronger light 

 on those points which have not hitherto received the full 

 attention that they deserve. 



The first thing to settle, in our opinion, is the real 

 nature or significance of the disease in the life-history 

 of the host. Is it a cause of bad health or the effect 

 of it ? Nine out of every ten foresters, and ten out of 

 every ten scientists, would probably say the former. Yet 

 we do not hesitate to question the accuracy of this opinion. 

 To explain our meaning quite clearly, it is necessary to 

 examine the somewhat ambiguous statement that a perfectly 

 healthy larch may be diseased. Most practical foresters 

 know that the great majority of thriving larch trees carry 

 blisters caused by Pezizi Wilkommi, and that these blis- 

 ters can exist without affecting the growth or commercial 

 value of the tree in the least. In such cases, therefore, 

 it may be said that healthy trees can also be diseased. But, 

 when practical men speak of diseased plantations, they 

 invariably refer to those cases where the growth of the 

 tree is apparently affected, and its market value is undoubt- 

 edly decreased by the presence of numerous blisters which 

 occur on stem and branches, and which cripple and deform 

 its entire habit of growth. As both of the above-cited 

 examples of blister attack may exist side by side, or within 



