INTRODUCTION 11 



he considers Theissen's Siigniatcaccae, founded upon insertion, to he a blun- 

 der (Ann. Myc. 16:35 1918). In the present key, all the genera that rest 

 upon such a character alone have been restored to their original position. 



ASCOMA AND PyCNIDIUM 



The usage with respect to criteria drawn from perithecium and apothe- 

 cium is long-established and fairly satisfactory, a statement that applies 

 almost equally to the pycnidium. This is especially true of texture, structure 

 of the wall, and the presence of ostiole, beak, stalk, and appendages or hairs. 

 Texture may afford a family character, as with the fleshy perithecium of 

 Hypocrcaccae or the gelatinous apothecium of the Bulgariaceae, but as a 

 rule it is generic in value as in the distinction between membranous and car- 

 bonous perithecia or pycnidia. In the case of structure, the radiate scutellum 

 marks the order Microthyrialcs, but within this generic distinctions are often 

 drawn on the kind or degree of such a structure. With regard to the ostiole, 

 presence or absence is usually generic ; however, in the Pcrisporiales absence 

 is characteristic of the order as a whole, while the form of the ostiole sets 

 apart the Lophiostomaceae and Hysteriaceae. In this connection, it should 

 be noted that Petrak has objected to Hoehnel's practice of utilizing the 

 presence or absence of ostiole in Phomalcs for generic segregation on the 

 grounds of great variability in this respect (Ann. Myc. 21 -.272 1923). 



The presence of a beak, stalk, hairs or appendages has been regularly 

 regarded as a warrant for generic segregation, and this has usually been 

 extended to marked differences in these structures, as for example in the 

 case of an oblique or lateral beak. Furthermore, with respect to hairs, usage 

 has also based distinctions upon the position, and even their color in the 

 case of the apothecium, but their arrangement is highly variable and 

 hence less valid for the perithecium. An exception to this occurs, how- 

 ever in the modified appendages of primitive ascocarps, such as those of 

 the Erysiphaccae. 



The grouping of perithecia has occasionally been employed for the erec- 

 tion of genera on the cespitose habit, and this though a doubtful character 

 has been utilized for the present. This character is often associated with the 

 presence of a subicle, with respect to which the practice of assigning generic 

 value has been generally accepted. In the Perisporiales and Microthyrialcs, 

 Theissen and Sydow have made much use of the presence or absence of a 

 free mycelium, as well as .its modification by means of hyphopodia and 

 spines, in which they have been followed for the present. 



In the Discomycetes, the absence of an exciple has been regularly 

 employed as a generic criterion, and this practice has here been followed in 

 essence, though such genera have been combined into a new family, Agyria- 

 ceae. The nature of the exciple has long been recognized as of basic value 

 among the lichens, the proper exciple without algal hosts being like that of 

 the other fungi and hence more primitive, while the thalline exciple with 

 algae is derived. The proper exciple is further distinguished as lecideine 



