400 THE DEUTEROMYCETES (FUNGI IMPERFECTI) 



spot of tobacco, are among the species of economic importance 

 not kno\\'n to possess a perfect stage. 



There are approximately 12 genera and 75 species of fungi 

 having peciiHar hehcal conidia. Some are entirely or partly hya- 

 line, and the others have yellow, brown, or dark fructifications. 

 This group has been monographed by Linder (1929). Many of 

 them occur on decaying wood and bark, imparting to it an effuse, 

 dark coating. Helicoma, Helicosporium, and Xenosporella are 

 among the most common representatives. Helicoma ciirtisli is 

 related to Lasiosphaeria pezizida, but connection with perfect 

 stages has not been definitely established in any others of this 

 group. 



Stilbaceae. The fungi that comprise the Stilbaceae are little 

 known even to the experienced mycologist. Possibly the most 

 familiar genera are Isaria and Graphium. Isaria is entomogenous. 

 It is constituted of species having hyaline synnemata with hya- 

 line, one-celled conidia that form over most of the surface of the 

 synnema. Some species have Cordyceps as their perfect stage, 

 whereas the perfect stage of others has not been observed. Isaria 

 jarinosa w^as long regarded as the conidial stage of Cordyceps 

 militaris. Fetch (1936), however, found that the two are not 

 connected, Cephalosporium being the conidial stage of C. mili- 

 taris. 



Graphium has dark-colored synnemata with dark, one-celled 

 conidia formed apically. This genus is best known through G. 

 iilmi, the cause of Graphium disease of elms (so-called Dutch elm 

 disease). This fungus has Ceratostomella idmi as its perfect stage. 

 A number of other species are associated with other species of 

 Ceratostemella, which cause "blue stain" of logs and lumber. 



TuBERCULARiACEAE. In this family the Genus Fusarium is of 

 outstanding interest. Its members are known to mycologists and 

 plant pathologists the world over, because they cause destructive 

 blights, wilts, and root rots of cereals, fiber plants, truck crops, 

 ornamentals, and woody plants. Its species are extremely diffi- 

 cult to identify, and consequently taxonomic problems have been 

 given a generous share of attention. These matters are ex- 

 tensively considered in the treatise by Reinking and WoUenweber 

 (1935). A somewhat different point of view is maintained by 

 Snyder and Hansen (1940, 1941). They studied the progeny of 



