CHAPTER X 

 ASCOMYCETES 



The Ascomycetes are those fungi in which meiosis takes place in 

 characteristic sporangia with endogenous spore formation. These 

 sporangia are called asci, their spores, ascospores. 



Their thallus is generally well developed and much branched; its 

 hyphae (in contrast to those of the Phycomycetes) are regularly divided 

 by septa into uni- or multinucleate cells. Under certain conditions of 

 nourishment, they may continue growth by sprouting; in some forms, 

 only sprout mycelium is known. 



The imperfect forms reach the culmination of development in this 

 group. Besides oidia, gemmae, etc. the most varied conidia have been 

 known which in part are joined into stromata, pycnidia, etc.; at times 

 these fructifications approach the perfect forms in size and luxuriance 

 of growth. In certain families, several of the imperfect forms may 

 appear successively or simultaneously on the same species (polymor- 

 phism). In case the corresponding perfect form is unknown, the imper- 

 fect forms are classified as Fungi Imperfecti and given special names; 

 for practical reasons these are occasionally retained in plant pathology, 

 even when the corresponding ascus form has been discovered, as often 

 only the imperfect forms are encountered. 



The sexual organs are inclined toward those of the Zygomycetes and, 

 like them, are formed as simple isogamous or heterogamous copulation 

 branches. In the higher forms, they undergo an extensive functional 

 and morphological differentiation: the male copulation branch becomes 

 an antheridium and the female an ascogonium. The antheridia gener- 

 ally exceed only by little the original size of the copulation branch, and 

 at most they coil helically. The ascogonia undergo specific further 

 development and in addition retain (or initiate) trichogynes; this cor- 

 responds functionally mutatis mutandis to the fertilization tubes of the 

 Oomycetes. In the simplest case, the sexual organs are arranged as 

 shown in Fig. 78: a unicellular antheridium approaches an also unicellu- 

 lar ascogonium and is surrounded by a trichogyne; thereby ascogonium 

 and trichogyne form the female copulation branch. 



Subsequently both the ascogonia and trichogynes may become multi- 

 cellular and coil characteristically and furthermore the ascogonia may 

 be borne on stipe cells; thereby arises a typical structure which earlier 

 was designated as Woronin's hypha, or scolecite. 



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