318 MANUAL OF TREE DISEASES 



touch each other. Small fruiting-bodies of the fungus causing 

 the disease are found biu-ied in the felt of mycelium. 



Cause. 



Three different species of fungi cause brown felt-blight of 

 conifers, namely : Herpotrichia nigra, common to Europe and 

 the United States on various conifers, except pines; Herpo- 

 trichia quinqueseptata, newly described on spruce in the North- 

 west; and Neopeckia CovMeri, found only on species of pines. 

 The effect of all three species is similar and they cannot 

 be distinguished except by microscopic examination of the 

 spores. 



The life history of these fungi is interesting. Only one 

 spore stage is known. The fruiting-bodies (perithecia) are 

 buried in the felt of mycelium and contain ascospores. The time 

 of infection is not definitely known but young seedlings and the 

 lower limbs which are buried in snow most of the winter are 

 the most generally affected parts. Whether infection takes 

 place under these conditions is a matter of conjecture. The 

 mycelium spreads very rapidly during the summer. A case 

 is described in which a branch of Alpine fir was entirely covered 

 by the growth of mycelium in a single season. The mycelium 

 enters the leaves and marked changes are brought about in the 

 mesophyl-tissue. An abundant growth of external mycelium 

 is also produced which covers the entire surface of the leaves 

 and twigs and binds them together into a mass. By the advance 

 of this epiphytic growth of mycelium over the surface of healthy 

 needles, it is possible that the fungus brings about humidity 

 relations which make possible the infection of the leaf and the 

 development of the internal feeding mycelium. Thus after 

 obtaining its start in a few needles buried in the snow, this fungus 

 may in this way prepare its own conditions for infection and 

 cause physiological changes in the leaves which render them 

 more susceptible. 



