CERATOSTOMATACEAE 203 



perithecia develop also in culture. The ascospores are peculiar 

 for the reason that on germination appressoria develop. 



The monographic treatment bv Griffith (1901), although old, 

 is very useful in any taxonomic study of the Fimetariaceae. That 

 by Seaver (1910) should also be employed. 



Sphaeriaceae. The Sphaeriaceae comprise some 20 or more 

 genera. The perithecia stand singly or in small groups, and their 

 bases may be immersed in a felt-like mesh or subiculum. The 

 perithecial walls are firm, and the ostiolar region is papillate. 

 Most of the numerous species are saprophytes on plant tissues, 

 especially Avood and bark, but a few are destructive pathogens. 

 Rosellinia deserves mention as typifying the parasitic species. 

 Rosellhiia qiiercina attacks oaks throughout Europe, being 

 especially destructive to seedlings and young trees in nurseries. 

 It forms strands of hyphae, rhizomorphs, characteristic of the 

 form Genus Dematophora. These strands ramify throughout the 

 cortex of the roots and extend throus^h the soil to contact the 

 roots of near-by seedHn^s. Black sclerotia, by means of which 

 the pathogen hibernates, also develop, both within the root tis- 

 sues that have been killed and at the exterior. Durino- the sum- 

 mer, conidia and perithecia form at the surface of affected roots 

 or on the soil. Details of perithecial development are wanting, 

 as they are for all other Sphaeriaceae. 



Rosellinia clavariae parasitizes Clavaria cinerea and other 

 species, giving to the bases of these coral fungi a blackened ap- 

 pearance. Its conidial stage has been identified as Helmintho- 

 sporiinn clavariorimi. 



Ceratostomataceae. The distinguishing feature of this family 

 is the presence of long, ostiolar beaks on the perithecia. Other- 

 wise the Ceratostomataceae resemble the Sphaeriaceae. Most 

 species are saprophytic. In the Genus Ceratostomella, however, 

 are several very destructive pathogens, as \\t\\ as certain others 

 commercially important because they stain lumber or logs that 

 have not yet been made into lumber. 



The most notable of the pathogens is Ceratostomella iihni, the 

 cause of Dutch elm disease. This disease was first recognized in 

 Holland and its causal agent described as Graphiinn iihiti, the 

 conidial stage, in 1922. Eight years later it was discovered on elms 

 in Cleveland, Ohio, and in Cincinnati, Ohio. Soon afterwards it 

 was located in the area surroundinij New York City, ^^ here it 



