PERENNIAL MYCELIUM OF PARASITIC FTJNGI 263 



The Gymno sporangium clavariforme occurs occasionally in 

 northeastern Iowa. The fun^s mycelium is found in the cor- 

 tex, breaking- out in elongated patches. The perennial character 

 of this fungus is well known. The G. nidus-avis also occurs in 

 northeastern Iowa. The mycelium of this is certainly perennial. 



The rust of Canada thistle (Puccinia suaveolens) (Pers) is 

 undoubtedly perennial. I do not recall its ever having been re- 

 corded for this state, but in sections of the country where the 

 host plant is abundant the rust is frequent. I am inclined to 

 think that TJromyces Glycyrrhizae is also perennial. 



The mycelium of Exaascus communis on Prunus hortulana is 

 described as perennial. This species is commonly found on the 

 young branches of this variety of plum. So far as the writer 

 has ob'Served, where this branch dies the fungus does not infect 

 new branches. The infection always comes from the spores of 

 tlie fungus. In some species at least in Exonsus deformans the 

 infection is said to take place at the time of the opening of the 

 buds. Duggar-" says; "but it may also result (occasionally) by 

 the growth of a perennial mycelium from the cJd wood, in which 

 it has rested over winter into the expanding peach buds." He 

 quotes Sadebeck as stating "the mycelium winters over in the 

 primary cortex and medullary tissues of the one-year-old 

 branches." This fungus is common in scmie seasons in Iowa. In 

 the case of E. co)nmunis the branches have always been found 

 dead, the fungus appearing only on new shoots. 



The cases of perennial mycelium of parasitic fungi are much 

 more common than plant pathologists at first thought. The per- 

 ennial mycelium of parasitic fungi is an important matter with 

 reference to the treatment of plant diseases. In some cases weeds 

 harbor the perennial mycelium of certain fungi and by destroy- 

 ing these weeds the injur^^ from the fungus may be greatly less- 

 ened. 



Department of Botany, 

 The State College. 



"FunsLis Diseases of Plants, 



