HEART-FOT IN CONfFERS. 43 



lings in the natural forest are presumably not so exposed to 

 damage. In my experience the following species are attacked 

 under such conditions : — European larch, Douglas fir, Japanese 

 larch, Norway spruce, Sitka spruce, Thuya gigantea, Tsuga 

 albertiana, Scots pine, and Abies grandis. 



Heart-rot is also abundant on old agricultural land and on 

 certain types of glacial drift soils, which are subject to extremes 

 of drought and moisture. No exact explanation has been given 

 of the true cause of these attacks on such types of soil. It is 

 possibly due to the fact that the subsoil conditions are not 

 suitable for the growth of tree roots, though forming no obstacle 

 to root penetration. 



There is some reason for believing, however, that certain 

 species are less liable to succumb under these conditions than 

 is the case with second crops on a stump-covered area. For 

 example, it is claimed that Douglas fir resists attack under 

 such conditions. In my experience the following species are 

 attacked on agricultural soils and on glacial drifts : — European 

 larch, Scots pine, Japanese larch, and Norway spruce. Though 

 not altogether unknown, the disease rarely occurs on young 

 trees of the broad-leaved species, which may be safely used for 

 old agricultural ground. 



If heart-rot is to be treated seriously, there are two lines 

 along which preventive measures may be developed ; firstly, 

 soil preparation, and, secondly, careful selection of species. 



Soil preparation might consist solely of removing old stumps 

 of previous crops. This has, of course, always been a serious 

 problem, and a very expensive undertaking. On light soils the 

 danger of leaving them is not so serious as on heavier ones. 

 Research might result in some chemical method by which the 

 toxic substances from decaying roots might be counteracted. 

 Perhaps when planting such areas it might be highly advisable 

 to give the stumps a fairly wide berth. In this way the young 

 plants would be placed further from the danger zones, while 

 more normal decay of the stumps might be induced. Protective 

 treatment of young plants before planting out might be under- 

 taken. If it be assumed, and the assumption seems a reasonable 

 one, that the process of transplanting, in the nursery and to the 

 forest, results in the death, decay ^and attack of some of the 

 roots of the young trees, it may be possible that the use of 

 seedlings in preference to transplants, at least on bare, recently 



