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



The fungus causing the disease in American houses is probably the 

 one described by Costantin and Dufour (1892c) and called Mycogone 

 perniciosa Magnus. Costantin (1893a) gives the morphological dif- 

 ferences between Mycogone rosea and Mycogone perniciosa, and, 

 although there has been no opportunity to compare our fungus with 

 the European species, it is thought that the two species are identical, 

 as the t T agree in both macroscopical and microscopical characters. 



INVESTIGATIONS OF THE MUSHROOM DISEASE IN AMERICA. 



TYPES OF THE DISEASE. 



During the course of the present investigation, specimens of the 

 two types or forms of infection as described by the French investi- 

 gators were collected in diseased mushroom houses in this country. 

 In many cases it was difficult to determine to which type the diseased 

 individuals belonged, as there are gradations between the two forms. 

 Often cap, stipe, and gills are clearly denned, the presence of the 

 malady being indicated by small tubercles on the cap and a fluffy 

 white growth on the gills, a form of the disease known in France 

 (Costantin and Dufour, 1892c, p. 471) as " chancre." 



In this country the common form of the disease is similar to that in 

 France. The mushrooms are covered with a white, velvety coating, 

 which consists of interwoven hyphse. This growth prevents the 

 normal development of the individual gills, which become more or 

 less coalescent, a condition shown in Plate I. The progress of the 

 disease is also frequently accompanied by arrested development and 

 by the distortion of the cap and stipe, as well as by the general 

 darkening and decay of the tissue. These characters are illustrated 

 in Plates II and III. 



In cases of infection termed by the French the " scleroderma 1 ' form, 

 the stipe is bulbous and the cap rudimentary or entirely lacking. In 

 this form the gills are completely aborted, and the diseased mushroom 

 is covered with a coating of interwoven hyphae similar to that of the 

 common form. It has been observed that in this form of the disease 

 the plants are much softer than in the other form and that they decay 

 more rapidly. Monstrous soft masses with thick white coatings of 

 the fungus are often observed in houses in which the disease is abun- 

 dant. These infected plants have very little resemblance to mush- 

 rooms, and they decay rapidly, forming a putrid mass which emits 

 a disagreeable, almost acrid odor. Figure 1 illustrates one of these 

 masses. Clumps greatly exceeding this in size are often found. 



MICROSCOPIC CHARACTERS OF THE FUNGUS. 



The small-spored VerticiUium described by Costantin and Dufour 

 (1892c) has not been observed in the specimens examined from 

 American houses, but it has been possible to grow the Mycogone in 



