364 THALLOPHYTES 



like the Yeast Plant, and the Molds which help in making cheese, 

 are useful. Some of the Ascomycetes are used directly as food. 

 The saprophytic forms are useful in hastening the decay of or- 

 ganic matter. But the main reason for their study is the desire 

 to be able to stop the destruction caused by the disease-producing 

 forms. 



The Ascomycetes are so named because of the ascus or sac 

 which is the characteristic spore-bearing structure of the group. 

 The ascus is an enlarged end of a hypha which becomes a thin 

 walled sac in which spores are produced. Any Fungus producing 

 spores in an ascus is called an Ascomycete. The spores produced 

 in an ascus are called ascospores. The Ascomycetes have other 

 spores, but the ascospores are the most general ones. 



The Ascomycetes differ from the Phy corny cetes in having no 

 zoospores and in having hyphae divided by cross walls. Many of 

 the Ascomycetes have sex organs and differentiated gametes, but 

 the cell resulting from fusion develops immediately into asci, so 

 there are no resting oospores to be considered in this group. 

 Taking care of the ascospores takes care of the results of fertili- 

 zation. 



The Ascomycetes vary widely in character of plant body and 

 methods of reproduction. In some the plant body is a structure 

 with a definite form, while in others it is only a scattered mass of 

 hyphae. In some the plant body is very prominent, but extremely 

 inconspicuous in others. Some have well-defined sex organs, 

 while others apparently have abandoned sexual reproduction and 

 have lost their sex organs. Their sex organs resemble those of 

 the Red Algae and this is the feature that suggests their relation- 

 ship to the Algae. There are about 15 orders and 29,000 species 

 of Ascomycetes. The Morels (Helvellales), Cup Fungi (Pezizales), 

 Closed Fungi (Pyrenomycetales) , Naked Ascus Fungi (Protodi 

 scales), Mildews (Peri sporiales), the Blue and Green Molds 

 (Plectascales) , and the Yeasts (Protoascales) are familiar orders. 



The Morels (Helvellales) . Not all of the Fungi of this order 

 are Morels, but the Morels are the most familiar ones. The 

 fleshy plant body with a definite form and often so large as to 

 be quite conspicuous is one of the notable features of the Hel- 

 vellales. They are mostly saprophytic and the mycelium usually 

 develops underground where it lives on decaying wood, leaves, 

 etc. Here belongs the Edible Morel shown on next page. 



