INJURIES INDUCED BY PLANTS 115 



pushed off when growth is resumed. Seedlings affected by 

 the blight usually perish, and can only recover when about 

 half of the leaves remain green and escape fresh infection. It 

 is decidedly inadvisable to make use of diseased yearling seed- 

 lings for planting. Neither is it advisable to use diseased 

 pines two years old and upwards, because they are usually 

 so weakened by transplanting that they soon perish. Diseased 

 plants on a regenerated area may, under favourable circum- 

 stances, recover from the disease. This, however, never happens 

 when the mycelium of the fungus has spread from the leaves 

 into the tissues of the stem itself. In particular, if the medulla 

 of the plant has become brown owing to the presence of the 

 mycelium, death supervenes, even although the buds look quite 

 healthy in spring. 



Should diseased leaves exist in the crowns of old pines, 

 infection may be easily induced by falling leaves. The young 

 plants are infected either by the dehiscence of the apothecia of 

 the diseased leaves that fall on them, or by the spores that are 

 conveyed to them from the diseased leaves in the descending 

 rain-drops. On this account it is not generally advisable to 

 form pine seed-beds under the drop of old pine-trees. 



Infection, in most cases, accompanies wind and rain which in 

 blowing over an infected area catches up numerous spores, and 

 bears them to sound plants. The experience that the disease is 

 most prevalent on very young plants, and in the case of older 

 ones only to a height of about two feet from the ground, is to be 

 explained by the fact that only the air-currents that are close to 

 the ground have the chance of catching up the spores of the 

 fungus and of depositing them upon plants. 



In order to raise healthy plants, it is advisable to form pine 

 seed-beds in dicotyledonous woods, or, at least, at as great a 

 distance as possible from young woods affected by the disease 

 of leaf-shedding. Nurseries for seedlings and transplanted trees 

 that have ever shown the disease should only be used for fresh 

 sowings after all diseased plants in the nursery itself, and in its 

 neighbourhood, have been destroyed. 



If one is compelled to form seed-beds in unhealthy districts, 

 one should select such situations as do not adjoin, at least on 

 the west side, young diseased woods. If the choice exists, it is 



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