TRICHOSPHAERIA PARASITIC A. 



471 



forms superficial white cushions on the white lines of stomata 

 of the needles. They therefore become discoloured, and at 

 length quite brown ; they do not, however, fall from the tree, 

 but hang down, being still attached to the twig by the mycelia 

 of the fungus. 



In November, on the brown cushions appear small globose 

 tomentose perithecia, con- 

 taining greyish spores, which 

 easily germinate when they 

 fall on twigs of silver-fir, and 

 the disease is thus spread. 

 The mycelium hibernates on 

 the twigs and needles and 

 grows again on to the new 

 spring-shoots, attacking the 

 needles from the base up- 

 wards, so that needles on the 

 older shoots which escaped 

 during the previous year 

 may now be attacked. 



Trees once attacked by this 

 fungus appear never to be- 

 come free from it, from 

 which its dangerous nature 

 is evident. 



b. Subjects of Attack, and 

 Distribution. 



Fig. 229. Twig of Silver-fir attacked by 

 . Trichosphaeria parasitica, R. Hrtg. 

 a Sound needles. 

 b Dead brown needles fixed to the twig 



by mycelial strands. 

 c Under surface of needles with white 



mycelia and dark sporocarps. 



This disease is widespread 

 in silver-fir forests and espe- 

 cially among 20 to 40 years old woods on the lower branches 

 and on advance-growth, and according to von Tubeuf, it also 

 attacks the spruce, but is rarer than on silver-fir. It has 

 done much damage in the Bavarian forests, near Passau and 

 other places. It has been noticed that lower branches of 

 silver-fir attacked by Trichosphaeria parasitica, E. Hrtg., 

 escape attacks by Corticium amorphum, Fr. (p. 454), when 

 neighbouring silver-fir are attacked by the latter fungus. 



