230 THE FUNGI WHICH CAUSE PLANT DISEASE 



Common in Europe on branches of Larix, Abies, Juniperus, 

 spruce and pine, doing great damage. The dark-brown mycelium 

 grows over the plant, killing and matting the leaves. 



Rosellinia Cesati & de Notaris (p. 226) 



Perithecia superficial, but often with the bases more or less 

 sunken in the substratum, coriaceous or car- 

 bonous; brittle, spherical or ovate, bristly or 

 not; asci cylindric, 8-spored; spores elliptic, 

 oblong or fusiform, 1-celled, brown or black; 

 paraphyses fusiform. Conidia of the type of 

 Coremium, Sporotrichum, etc. 



In most cases the active parasitic stage 



occurs on roots and consists of a vigorous 



white mycelium, which remains for a long time 



Fig. 164. — Herpotri- sterile, developing large branching and inter- 



c, spore. After lacing rhizomorphs (Dematophora) which later 



Winter. become brown. These resemble somewhat, but 



are distinguishable from, the rhizomorphs of Armillaria mellea; 



again, they are Rhizoctonia-like. 



There are over one hundred seventy species, mostly saprophytic. 

 R. necatrix (Hart.) Berl.""' "^ 



A destructive fungus, long known as Dematophora necatrix, 

 possesses a white mycelium which invades the small roots, thence 

 passes to larger ones, extending in trees through the cambium 

 and wood to the trunk, occasionally rupturing the bark and pro- 

 ducing white floccose tufts. Sclerotia of one or more kinds are 

 produced in the bark and often give rise to conidia on tufted conidi- 

 ophores in a Coremium-like layer (Fig. 165). The mycelium, 

 when old, turns brown and produces large branching, interlacing 

 rhizomophic strands which spread to the soil, or wind about the 

 roots. 



In some instances the connection of the ascigerous with the 

 sterile or conidial stages is well established; in others the asci 

 have been found but rarely and the evidence of genetic connection 

 is not complete. It is probable that some fungi reported as Dema- 

 tophora do not in reality belong to Rosellinia. 

 The fungus attacks nearly all kinds of plants. 



