602 FUNGI IMPERFECTi: THE IMPERFECT FUNGI 



that those forms belong to Class Basidiomyceteae, their absence in very- 

 many cases may or may not indicate that they belong elsewhere. The form 

 genus Sclerotium includes species producing sclerotia with more or less 

 definite form, usually light-colored internally and Avith a brown or black 

 rind. For many forms only the sclerotia and associated mycelium are 

 known, but many similar sclerotia produce apothecia (Sclerotinia in the 

 Pezizales) or basidiomycetous spore fruits {Typhula in Family Clavari- 

 aceae). Pachyma is an enormous subterranean sclerotium, more or less 

 fibrous-fleshy internally and rough or irregular externally. P. cocos Fr., the 

 tuckahoe, sometimes larger than a man's head, was formerly used for food 

 by the Indians inhabiting the regions now comprised by Virginia and 

 adjacent states. Its perfect stage is a species oiPolyporus which grows out 

 of the sclerotium. Rhizoctonia consists of superficial, irregular, scale-like, 

 black sclerotia growing on the surface of the subterranean portions of the 

 host plant, these being preceded and accompanied by a superficial dark- 

 colored, short-celled, abundantly branching, rather stout mycelium. This 

 mycelium is entirely different in appearance from the slender, hyaline 

 mycelium growing within the host tissues. The perfect stage of Rhizoc- 

 tonia solani Kiihn is Pellicularia filamentosa (Pat.) Rogers, more com- 

 monly referred to as Corticium vagum var. solani Burt ex Rolfs, or C. 

 solani (Prill. & Del.) Bourd. & Galz., Family Thelephoraceae. It is a very 

 destructive enemy of many species of cultivated plants as well as of a 

 large number of wild plants. Rhizomorpha is the name given to strands of 

 mycelium, dark externally and usually white internally. R. suhcorticalis 

 Pers. consists of the rhizomorphs of Armillariella mellea (Dahl) Karst., 

 Family Agaricaceae. Ozonium consists of loose masses of usually bright- 

 colored mycelium, frequently united into strands and again spreading 

 out. Some species are parasitic, others saprophytic. 0. omnivorum Shear, 

 destructive to cotton and many other cultivated as well as wild plants in 

 Texas and adjacent states, spreads through the soil and attacks the roots 

 of the host plants. It sometimes produces a conidial stage, Phymato- 

 trichum omnivorum (Shear) Duggar, mentioned earlier in this chapter. 

 Once a species of Hydnum was found associated with it (Shear, 1925), but 

 its connection with this fungus has not been demonstrated beyond 

 question. 



Penicillin, Streptomycin, and Other Antibiotics 



Bacteriologists and students of fungi have observed for years that 

 frequently in cultures of organisms certain contaminating species of 

 Penicillium, Aspergillus, and other molds would destroy the adjacent 

 portions of the colonies of bacteria or fungi. Dr. Alexander Fleming had 

 such an experience in 1928, but instead of discarding his culture of Staph- 

 ylococcus as spoiled and useless, he began a study of the contaminant and 

 of the antibiotic substance that it produced. It proved to be a species of 



