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 Phycomycetes 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 odspores 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. 
