THE FUNGI WHICH CAUSE PLANT DISEASE 663 



lenticels. Inside of the host tissue the mycelium is not tjrpically 

 associated to form strands and its cells are hyaline. 



The fungus was in early studies difficult to isolate but Atkinson 

 in 1893 *^ obtained pure cultures by rinsing the diseased roots in 

 distilled water, cutting in small pieces and placing on sterile filter 

 paper lying on sterile sand in a moist chamber. In a few days the 

 strands grew over the paper onto sterilized slides. Bits of sterilized 

 cotton-root were then placed in contact with the advancing hyphse. 

 Soon the new culture thus secured could be transferred at will. 

 A slight acidity retards bacterial growth and renders isolation of 

 the Ozonium less difficult. In culture sclerotia about 3 mm. in 

 diameter, whitish and woolly, later brown, appear. 



Xylostroma Tode (p. 659) 



This occurs, forming thick, felt-like layers, in cracks of timber. 

 It is regarded as the mycelium of various Hymenomycetes, es- 

 pecially Fomes. 



Fungi of Unknown Affinity 



The following imperfectly known genera do not fit readily into 

 the scheme of classification and are all in need of careful study. 



Acrocystis Ellis & Halsted 



Monotypic; though technically a nomen nudem, the illustrations 

 are recognizable. Examination of the original material shows 

 Saccardo's reference to the Mucorales to be untenable. 



A. batatae E. & H.^* 



Hyphae uitercellular, branched, producing enlarged cysts at the 

 ends of branches, the nature of these unknown; enlarged, intra- 

 mycelial swellings contain numerous rounded conidia. 



It is described as the cause of soil rot of sweet potatoes. 



Graphiola Poit 



Mycelium within the host; fruiting body rotund, carbonous 

 duplex, the outer layer of interwoven branched hyphae, firm, in- 



