40 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



another by ariificial mycelial infection, i.e., by extracting a piece 

 of diseased tissue, containing the mycelium, from an infected 

 tree, and inserting it into a healthy one. Shortly after the 

 cortical tissue has been killed, small yellow- white pustules, about 

 the size of a pin-head, appear. Thes6 are the stromata of the 

 parasite. They produce a number of conidiaphoi'es, either on the 

 surface or in the interior of these cushions. The conidiaphores 

 are erect branches of the mycelium, and at their apices the 

 conidia are to be found. These are supposed to be leproductive 

 bodies, but nobody has as yet succeeded in getting ihem to 

 germinate on the tree. The stromata are very sensitive to 

 draught, and in a dry atmosphere are quickly shrivelled up and 

 killed. If the atmosphere be moist enough, the well-known 

 ascophores subsequently make their appearance on the same 

 places. The beautiful colours of these bodies are well known. 



We have already seen that the mycelium enters and kills the 

 living tissues of the " bark " and wood-body, and this explains 

 why one or a few small blisters may seriously interfere with the 

 growth of the whole stem. On parts of the tree which have 

 been killed, numerous ascophores may bi'eak out on the bark at 

 places where no blister previously existed. 



The disease has existed in the Alps from time immemorial, 

 but the only places where it becomes epidemic there, are in the 

 moist, damp valleys, and in the neighbourhood of lakes. On the 

 exposed slopes the free circulation of the atmosphere to a large 

 extent prevents the production of ascophores. These bodies only 

 appear near the base of the tree, or on cankered branches, when 

 these are lying on the ground, because the surrounding grass and 

 other vegetation prevent the free circulation of the air, and 

 favour the growth of the young fructifications. 



During the early decades of last century, the larch was ex- 

 perimentally cultivated here and there in Germany, with very 

 satisfactory results, which led to its cultivation all over the 

 country ; but after smaller and lai'ger plantations had been 

 formed, from the foot of the Alps to the coasts of the North Sea and 

 Baltic, it was followed by its parasitic enemy, which found the 

 conditions on the low ground veiy favourable for its develop- 

 ment. At first large pure woods of larch were formed. Larch 

 was also used to fill up gaps in older beech plantations, ana it 

 was farther cultivated in places with moist, stagnant air. In 

 addition to this, infected specimens were sent out from the 



