16 CIRCULAR NO. 127, BUREAU OF PLANT INDUSTRY. 



DESCRIPTION OF THE FUNGUS. 



The fungus causing silver scurf has two more or less markedly dis- 

 tinct stages in its development: The brown-mold stage (fig. 1, o, 

 b, and c), which appears first and consists of the conidiophores and 

 conidia, and the sclerotial stage, wdiich follows later and consists of 

 numerous small black sclerotia biiiied in the outer cells of the dis- 



FiG. 1. — Tho brown mold stage nf Spondylocladium AtrovircTis. (a) The fruiting organs of the fungus. 

 (6) A portion of conidiophore with attached conidia. (c) The several-celled .spores, which usually put 

 out a germ tul^e fron. the pointed end of the spore. (After Appel and Laubert.) 



colored areas. The relation of the sclerotia to the cells of the outer 

 skin of the potato is shown in figure 4. \Yhen viable s})ores are 

 placed in water at room tem])erature, they push out germ tubes in 

 the manner shown in figure 1, c. Thes(^ may ])enetrate the periderm 

 and later the ])arcnchyma, according to Frank. It has been reported 

 by Johnson tliat sclerotia are even j^rochiced in the cells of the paren- 

 chyma and that the fungus gi-ows readily on the cut surface of the 

 potato. The wTiter has also observed the fungus fruiting on cut sur- 



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