257 



the wood. Perithecia ovate-coriical, very black and superficial, about i mm. 

 in diameter, clothed with very minute black bristles about 20-30 microns 

 in length. 



Asci (p sp.) 8-10x65-70 microns. 



Spores 7-8.75 x 10-14 microns. 



Common on Fraxinus and Ostrya near Bloomington, Ind. Found on 

 decorticated wood and underneath loosened bark. 



PtOSELLINIA AS A PARASITE. 



Unlike Hypoxyllon and Nummularia, Rosellinia is of great economic 

 importance on account of several of its species being active parasites. 

 Of the one hundred seventy species now described, at least eight are known 

 to be injurious and destructive to living plants. Xo doubt many other 

 species will be found to be parasitic when a more thorough study is made 

 of them. The following is a brief account of some of the most destructive 

 species : 



BoselUma quercina Hart. Perithecia scattered, seated on a black 

 mycelium, black globase, about 1 mm. in diameter. Asci sub-cylindrical, 

 eight spored, 8-10 x 160-170 microns. Spores brown, acute at both ends, 

 6-7 x 28 microns. 



This species is called the oak root fungus, and attacks the roots of 

 seedling oaks that are from one to three years old. The mycelium spreads 

 rapidly through the ground from one plant to another and is especially 

 destructive during warm, damp weather. This mycelial form was formerly 

 referred to a special genus, Rhizoctouia. The effects of the fungus are 

 first shown by the wilting and drying of the leaves near the top, the lower 

 ones following in order until the whole plant is killed. If a seedling so 

 affected is pulled up and the roots examined, a fine, thread-like mass of 

 wbite mycelium will be found completely enveloping the roots. The tap 

 root will have dark ovoid bodies about the size of a pin head where the 

 lateral roots join. The tap root is often quite rotten where the mycelium 

 has enveloped it, and especially in the neighborhood of the black tubers. 

 Numerous black sclerotia are found on the surface of the dead roots. The 

 strands of mycelium readily penetrate the young rootlets not yet protected 

 by a layer of periderm and may kill the plant in from ten to fifteen days 

 Slender hyaline conidiospores are usually found near the base of the stem 

 and on the adjoining soil. Later the perithecia are formed on the dense 

 mass of mycelium covering the superficial roots. 



17— 49C<; 



