CHAPTER XIII 

 EUASCOMYCETES 



The Euascomycetes differ from the Hemiascomycetes in that the 

 zygotes develop first to ascogenous hyphae which then proceed to the 

 formation of asci. Parellel with this formation of ascogenous hyphae, 

 there generally develops ascigerous fructifications whose morphological 

 relationships form the basis of the systematic classification of this 

 subclass. 



Originally the Euascomycetes were divided into four orders which 

 may be regarded as the four historical orders, the Pyrenomycetes with 

 perithecia, the Discomycetes with apothecia, the Tuberales with hypo- 

 gaeous tuberiform fructifications and the entomophilous Laboulbeniales 

 with a modification of the perithecia. Recently the Pyrenomycetes, 

 and Discomycetes have been extensively subdivided on the basis of the 

 manner of opening of the fructifications and the arrangement of the asci. 

 The cleistocarpous Pyrenomycetes, in which the ascospores are only 

 liberated by a decay of the perithecia, are assembled in the Plectascales 

 Perisporiales and Myriangiales. The higher Pyrenomycetes, however, 

 in which generally the liberation or discharge of ascospores is facilitated 

 or made possible by the formation of a special opening, are grouped in the 

 Hypocreales, Sphaeriales, Dothideales, Hysteriales and Hemisphaeriales. 

 The Discomycetes are divided into the Phacidiales, in which the apothe- 

 cial covering is only ruptured at maturity, and the Pezizales, in which it 

 is generally reduced to threads during the development of the 

 apothecia. Thus in the classification followed here the Euascomycetes 

 include 12 orders whose characters will appear in the course of the 

 discussion and whose probable morphological relations are graphically 

 represented in the collective scheme at the close of the book (p. 618). 



PLECTASCALES 



Among the typical Ascomycetes the Plectascales are characterized 

 by the possession of angiocarpous perithecia without ostioles, whose 

 interior is irregularly penetrated by ascogenous hyphae, consequently 

 the asci (generally spherical) lie scattered irregularly in the ground tissue 

 of the fructification. The peripheral layers of the fructifications may 

 thicken to a pseudoparenchymatous rind which, in the lower forms, gradu- 

 ally degenerates at maturity. 



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