CHAPTER VII 



THE FUNGI : ASCOMYCETES AND BASIDIOMYCETES 



ASCOMYCETES 



The Ascomycetes are Fungi whose fruiting bodies are either composed of 

 interwoven filaments or of a pseudoparenchyma consisting of a compact 

 tissue of filaments. They may be sac-like perithecia, either completely 

 closed or flask-shaped and opening by an ostiole, or even open cups^ 

 apothecia. Within the fruiting bodies sac-shaped asci are developed, in 

 which eight (sometimes four or sixteen) ascospores are formed. The 

 spores are forcibly ejected from the asci and form new mycelia. The asci 

 may originate from the fusion of nuclei, derived from an oogonium and 

 antheridium, but in many instances there has been a great degeneration of 

 the sex organs, and sexual conjugation consists simply in the fusion of two 

 vegetative nuclei. In the Ascomycetes the oogonium is frequently called 

 the ascogonium from the fact that it produces asci. Asexual reproduction 

 is by conidiospores. Many species are of great economic importance as 

 the cause of serious plant diseases. 



The Ascomycetes are divided into a number of orders of which we shall 

 consider examples of the following : — 



1. Plectascales {e.g., Aspergillus). 



2. Erysiphales {e.g., Sphaerotheca, Erysiphe). 



3. Pezizales {e.g., Pyronema, Pezizd). 



4. Helvellales [e.g., Helvella). 



5. Phacidiales {e.g., Rhytisma). 



6. Saccharomycetales {e.g., Saccharomyces). 



7. Hypocreales {e.g., Claviceps). 



8. Sphaeriales {e.g., Hypoxylon). 



9. Laboulbeniales {e.g., Stigmatomyces). 



Plectascales 



The Plectascales are Ascomycetes in which the product of the fertilization 

 of the ascogonium is frequently only a single ascus. In some of the higher 

 members, where more than a single ascus is produced, the asci are not 

 arranged in any system, but are scattered irregularly in a special closed body 

 termed the perithecium. 



We shall consider one example of this order, Aspergillus. 



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