DISEASES DUE TO SOIL-INFLUENCE 277 



found to be wet and rotten almost back to the stool, while on the 

 other hand all or most of the shallow lateral roots remain per- 

 fectly sound. Only in rare cases is the withering of the tree due 

 to saturation of the stool with resin, consequent on the decay of 

 the tap-root. Root-rot is to be distinguished from the ravages 

 of Trametes radiciperda both being frequently met together 

 in pine woods by the tap-root rotting and the lateral roots 

 remaining sound, whereas in the case of the parasite the tree 

 is killed, though not thrown, owing to the lateral roots being 

 attacked. 



The disease is also to be met with in spruce woods growing 

 on decidedly shallow soils that contain stagnant water. Under 

 such circumstances, however, it is less destructive, because the 

 shallower root-system of the spruce makes the tree more 

 independent of the decay of the few roots that penetrate deep 

 into the soil. 



In the case of pine woods, root-rot appears only on soils 

 where, at a short distance from the surface (usually about i\ ft), a 

 stratum is encountered which offers no obstacle to the entrance 

 of the tap-root when the trees are young, but which is of such a 

 texture as to prevent the free circulation of air after the wood 

 has become close. This stratum, which usually consists of 

 argillaceous loam or of very fine-grained quartz (alluvial loam), 

 is so difficult to work with the spade as to necessitate the use of 

 the pick. As such conditions of soil are also unsuitable for 

 agricultural purposes, we very frequently find such strata where 

 farming has been replaced by forestry. For this reason the 

 subsequent disease of the pines has been erroneously ascribed 

 to the previous tillage operations. At first young pine woods 

 thrive admirably on such soils. The tap-roots penetrate to the 

 deeper layers of the soil, to which at first the circulation of air 

 also extends. It is only when the branches begin to interlace 

 and to form a dense umbrageous canopy which protects the 

 soil summer and winter, and when a thick layer of leaves and 

 humus forms on the ground, that the circulation of air in the 

 soil is interfered with. Insolation becomes impossible, and both 

 heating and cooling are rendered alike difficult. As the soil 

 remains constantly moist, while the air is largely excluded from 

 soil that is argillaceous and very impervious, or consists of dense 



