n8 DISEASES OF TREES 



numerously represented, that it is at first surprising why it does 

 hardly any damage there. This is easily explained from the 

 fact that at high elevations the transition from winter to 

 spring is very rapid, and the development of the leaf-fascicles 

 occupies but a short time. On the plains the larch begins to 

 display green buds even towards the end of March, but their 

 further development is often retarded for a long time, until, 

 in the beginning of May, the growth of the leaves pro- 

 gresses more rapidly. This is the dangerous period for the 

 larch, because when the caterpillars awake from hiberna- 

 tion they begin to devour the green buds, and when growth 

 proceeds slowly these are largely consumed, and the trees 

 are, for the most part, defoliated. On the other hand, when 

 the leaf-fascicles develop rapidly, a small proportion of the 

 foliage suffices to feed the caterpillars. In Alpine regions 

 the short spring saves the larches from complete or excessive 

 defoliation, which, especially when often repeated, results in the 

 crippling and death of the trees. The Larch Aphis also, 

 Chennes Laricis, damages the foliage of the larch to no small 

 extent, though not nearly so much as the moth. The disease 

 which is induced by P. Willkommii differs entirely from the 

 crippling which larches experience as a result of the attack of 

 the moth, aphis, &c. This parasite is indigenous to high Alpine 

 regions, where it produces the same disease that has resulted in 

 the destruction of innumerable woods in Germany, Denmark, 

 and Scotland. In its native habitat, however, it is only under 

 special conditions of environment that it destroys whole woods. 

 In order correctly to appreciate this point we must first review 

 the course of development of the parasite. 



The spores which originate in cup-shaped fructifications to 

 be afterwards described soon germinate in the presence of 

 sufficient moisture, with effect not on an uninjured tree, however, 

 but only on a wound. Such wounds are very often due to hail- 

 stones, or to the dwarf-shoots being devoured in spring as was 

 mentioned above or they are formed in the upper angle of 

 the base of a branch (Fig. 58, U) owing to its depression under 

 accumulations of snow or hoar-frost. From such wounds the 

 vigorous, copiously ramifying, septate mycelium spreads in the 

 soft bast, partly between and partly in the cells advancing in 



