CHAPTER V 



CLASS II. ASCOMYCETES 

 {The spore-sac Fungi.') 



The members of the second class of Fungi, the Ascomycetes, 

 are characterized by their method of producing spores in dehcate 

 membranous sacs called asci. These asci, at least in the higher 

 forms are collected together in a body which may be spherical, 

 flask-like, cup-shaped or disc-like ; this body is variously known in 

 the different orders as a perithecium, an ascoma, a receptacle or 

 an apothecium. We may speak of it in general as an ascocarp. 

 Mixed with the asci are simple or branched bodies known as the 

 paraphyses. {PI. 4, f. 10.) The ascomycetes vary greatly in 

 size, habit and structure ; mycelium is usually abundantly de- 

 veloped and is usually branched and with cells clearly marked 

 by transverse septa or partition walls. The mycelium is arach- 

 noid (cobwebby) in a few forms, but in most species it is usually 

 concealed or buried, while the spore-producing body becomes 

 the conspicuous feature of the plant. In size the members of this 

 class of fungi range from one-celled organisms, like the yeast 

 plant floating in a liquid medium, to large fleshy forms several 

 inches in height, or in some cases hard, almost woody structures 

 are developed, forming conspicuous masses. Most, however, are 

 inconspicuous members of the plant world. Many of them are 

 saprophytic, living in rich soil, or more commonly on dead stems 

 or trunks of trees ; a few are subterranean ; a number of fleshy 

 forms are edible, like the morel and trufl^es. A large number of 

 forms are parasitic and produce a variety of diseases among culti- 

 vated plants like the leaf curl of the peach, plum pockets, the 

 black knot of the cherry and plum, and the various powdery 

 mildews. 



Besides the ascospores, many species produce conidia which 

 are developed in a great variety of ways ; some also produce 

 pycnidia and occasionally other forms of reproductive bodies are 



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