THE PREVALENCE OF FOMES ANNOSUS. II7 



very remarkable in general forestry practice in this 

 country. It is a mistaken policy. Apart from their 

 ability to resist the root fungus, they also tend to 

 counteract soil acidity. Again, who is able to forecast 

 the demands of future generations? 

 6. When the soil is so poor as to be quite unsuited to 

 hardwoods, as on peat or on very unfertile soils, it 

 is probably best to plant Scots pine and to leave the 

 trees to make the best of things. The possibilities of 

 birch should not be overlooked. 



Some attention to the above rules would certainly restrict 

 the attacking power of Forties a?inosus. Something may be 

 attempted to mitigate the damage in a growing wood. If the 

 attack is very severe, the best plan is to let in the air by 

 a heavy thinning — which at the same time strengthens the 

 individual trees — so that the accumulated humic acid of the 

 upper soil layers may be removed by oxidation. In the case 

 of slight attacks, a light thinning of the weakest trees would 

 be beneficial. If thinning does no good, the wood should 

 be clear felled and planted with suitable trees. A short 

 rotation of hardwood might even be advisable. 



It seems that the fungus only lives in the upper soil layers 

 into which the spores may be carried by rabbits and other 

 animals, or washed by rainwater from the bases of the stand- 

 ing trees. It is in the upper soil layers where the greatest 

 concentration of acid takes place, and where the greatest 

 damage to the rootlets probably occurs. It is thus important 

 to be able to tell whether the acid accumulation in the soil 

 is excessive or not. It will be seen that such an accumulation 

 is in great measure dependent on the density of the canopy, 

 so that a careful study of crop density in relation to root 

 diseases caused by fungi is indicated as important. 



