112 DISEASES OF TREES 



withered on the side of the tree which is exposed to wind or sun. 

 One should certainly not ascribe the withering of spruce-leaves 

 during winter on the sunny side of the tree to the action of frost, 

 and there is quite as little reason for relegating to the same 

 cause the browning of young pines in frozen ground owing to 

 direct insolation and strong air-currents. 



In the height of summer, about the month of July, exactly the 

 same phenomenon may be observed during dry weather when 

 pines in a drilled seed-bed on sandy soil are left standing for a 

 second year. Only those pines remain perfectly healthy which are 

 situated at the sides of the paths that is to say, at the edges of 

 the beds. In spring the one-year-old pines remain quite healthy, 

 as long as the soil retains a sufficient supply of moisture and 

 growth has not begun. Afterwards growth proceeds both above 

 and below ground, though most vigorously in the marginal 

 plants, whose roots can obtain water and nutriment from the 

 paths as well as from the bed. Should transpiration of water by 

 the plants in July be greatly increased partly in consequence of 

 the air being dry and warm, and partly owing to the formation 

 of new shoots and leaves ; and, on the other hand, should the 

 soil have lost its winter moisture, then the pines wither in exactly 

 the same way as happens in winter when the ground is frozen 

 and the sky is clear. Only those plants remain green which 

 stand nearest to the paths, or at least to the edge of the bed. 



In the nursery at Eberswalde, after a severe early frost in 

 October, that portion of the ground of the pine seed-beds which 

 the sun could not reach was still frost-bound at midday. On 

 the other hand, the ground which the rays of the sun could affect 

 was completely thawed and warmed in the course of the fore- 

 noon. The seed-beds all over were beautifully green, and very 

 healthy. 



A few days later all the pines in the seed-beds which had been 

 shaded were brown, whereas those which had been exposed to 

 the sun remained perfectly healthy. I am able to explain this 

 phenomenon only by the fact that the frozen ground prevented 

 the absorption of water by the roots, whereas the clear sky and 

 relatively warm air furthered transpiration by the leaves. In 

 this case shading had acted prejudicially. 



In by far the greater number of cases the pine leaf-cast is 



