INJURIES INDUCED BY PLANTS 121 



abortive gonidia, or are to be classed with spermatia, remains, 

 in the meantime, undetermined. In this place it is specially 

 important to emphasise the fact that they are incapable of 

 assisting in the distribution of the parasite. 



The small stromata are very readily affected by a dry atmo- 

 sphere and by air-currents, in which they quickly wither and die. 

 They develop only when constantly surrounded by moist air 

 Under such circumstances they produce the well-known cup- 

 shaped ascocarps (Fig. 60, b &). These possess a hymenium 

 of a fine red colour. The hymenium consists of innumer- 

 able asci surrounded by filamentous paraphyses. Eight colour- 

 less spores are formed in the interior of each ascus. The fact 

 that the mycelium penetrates even into the wood, and kills it, 

 explains why one or a few small blisters may greatly interfere 

 with the growth of the whole stem. Numerous cup-shaped 

 ascocarps ultimately make their appearance on the dead cortex, 

 and these are met with even when blisters are absent. 



In muggy situations the larches soon become diseased, and die 

 in a few years without any large blisters making their appear- 

 ance. The cup-shaped ascocarps of the parasite appear upon the 

 cortex. It looks as though the large quantity of water present in 

 larches whose transpiration is interfered with greatly favours the 

 development and spread of the fungus in the wood, and that the 

 disease consequently spreads throughout the whole plant. 



The foregoing descriptive sketch of the results of my investiga- 

 tions may suffice to explain the recognized facts connected with 

 the occurrence and distribution of the disease. 



The larch-blister has been indigenous to high Alpine regions 

 from time immemorial. It occurs, however, with marked in- 

 tensity only in damp muggy valleys in immediate proximity to 

 lakes (e.g. the Achensee in the Tyrol, &c.), though on plateaus 

 it may also destroy a small tree here and there. Owing to the 

 prevalence of air-currents, freely exposed ascocarps never ripen 

 on plateaus and valley-slopes. The ascocarps ripen only on 

 those blisters which are situated at the foot of the stem close to 

 the ground, or on blistered branches that are in contact with the 

 earth. This is owing to the surrounding high grass sheltering the 

 young ascocarps against air-currents, and so keeping them moist. 



In the early decades of this century, when the larch was planted 



