Chapter 6 

 THE ASCOMYCETES 



The Ascomycetes, or sac fungi, comprise between 25,000 and 

 35,000 species. They possess a multiplicity and complexity of 

 architectural design and a seemingly infinite variety of patterns 

 of activity that are baffling to all who attempt to catalogue or to 

 orient them. It is an all too common experience of the mycolo- 

 gist, after having studied a group of kindred forms, to encounter 

 one which appears to be related to the others and therefore to 

 anticipate that its behavior will be similar. He may find to his 

 surprise, however, after intimate acquaintance, that the appar- 

 ently similar species is entirely distinct and that it does not fit into 

 the niche into which he anticipated it would fall. If he then 

 attempts to console himself for this error in judgment, he may 

 arrive at the sage conclusion that no Emily Postian rules of con- 

 duct exist for the guidance of Ascomycetes; and, even if they 

 did, all fungi are illiterate and hence unable to determine how 

 thev are supposed to behave. 



AssLMiLATORY PHASE. The thallus of Ascomycetes generally 

 consists of septate hyphae, more or less entangled, each cell of 

 which is usually uninucleate. In some the hyphal cells separate 

 with age, forming oidia, or become thick-walled, forming chlamy- 

 dospores. In others the hyphae become compactly aggregated 

 into sclerotia or stromata, in a\ hich stage the species is able to 

 survive periods of stress or to hibernate. In certain species the 

 hyphae themselves perennate within twigs or buds. 



Asexual reproduction. A large number of Ascomycetes have 

 one or more asexual or conidial stashes bv means of which they 

 propagate and disseminate themselves. Sometimes the conidia 

 are able to survive from one season to the next. The fact that a 

 conidial fungus can hibernate, it may be pointed out, does not 

 constitute evidence that it lacks an ascogenous stage. Many 

 ors^anisms are know only in the conidial stage, especially among 

 pathogenic species. Similarly many fungi are know^n in the asco- 



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