4 BULLETIN 127, U. S. DEPARTMENT OF AGRICULTURE. 



It was at first thought that there were two different diseases, but 

 when a sufficient number of specimens were studied all transitions 

 between the two forms of Verticillium were found and it was estab- 

 lished that it was one disease with two very dissimilar forms of 

 fruiting bodies. 



Costantin explained that, together with Dufour, he had previously 

 stated, that the fungus was similar to Mycogone cervina, but that 

 they had not identified it with that species. The fungus also did 

 not agree with the description of Mycogone rosea. 



Costantin and Dufour (1892c and 1893a) give the most exhaus- 

 tive study of this disease of cultivated mushrooms. They discuss 

 the two characteristic types of infection, as described in their pre- 

 vious article, designating them as the common form and the sclero- 

 derma or puff ball-like form. The discussion of the fungus immedi- 

 ately following embodies the observations made by these authors. 

 A microscopic examination of the common form, as previously 

 described, revealed the presence of a Verticillium having large spores 

 variable in size and form. The large spores are two celled, 18 to 

 20 by 3.5 u, while the small spores are more numerous and one 

 celled, 8 by 3 <i. This Verticillium is usually found on the gills in 

 an early stage of the disease. At a later stage of the disease the 

 mushroom is covered with a thick white coating consisting of long 

 irregularly and verticillately branched hyphas, upon which are borne 

 bicellular u chlamydospores ' ' of a Mycogone. In rare cases these 

 large Mycogone spores are three celled and much longer than the 

 usual 2-celled spores. At first these two cells are smooth, hyaline, 

 or colorless, and almost equal in size; later the terminal cell becomes 

 swollen, amber colored, and covered with warts. It is spherical hi 

 shape and measures about 16 to 20 ,«. The lower or basal cell is 

 smaller, smooth, colorless, and 14 to 16 ,« in size. 



In specimens of the puffb all-like type of infection the color is at 

 first a dirty white, becoming pearl gray or pale rose gray as the 

 disease advances. In this latter stage the deformed mushroom is 

 covered with a light velvety tomentum or hairhke coating formed 

 of little tufts or filaments much more branched and scattered and 

 thinner, but still of the form of Verticillium. The spores are uni- 

 cellular, more numerous than the form just described, and much 

 smaller, being 4 by 2 pt in size. 



Magnus (1906), Cooke (1889), and Prillieux (1892) probably 

 observed the disease in the common form, i. e., the Verticillium 

 with large spores and the Mycogone spores, while Stapf (1889), who 

 reported only a Verticillium stage, examined the disease in the 

 puffball-like stage, where only the Verticillium with small spores 

 was present. 



