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CLASSIFICATION
rooms. In his Systema Mycologicum, Fries placed nearly all the mushrooms in
the genus Agaricus but he divided the genus into a number of sections such as
Lepiota, Tricholoma, Pholiota, Psalliota, etc. Later authors raised these sec-
tions to the rank of genera, but the old name Agaricus had to be retained for
one of these sections, depending on what was considered to be the type species
of Agaricus. Since the common meadow mushroom, Agaricus campestris, is
taken as the type, the name Agaricus must be used for it and its close relatives.
The name Psalliota, which was used by Fries for this section and by some later
authors as a generic name, then becomes a synonym of Agaricus and is no
longer a legitimate name.
In this book a number of species may be found under unfamiliar names.
Some of the changes are the result of advances in our knowledge and of con-
sequent improvements in the classification. For example, it is beheved that it is
a better expression of relationships to remove the species with granulose caps
from Lepiota to Cystoderma, and the species with viscid caps from Lepiota to
Limacella. Other changes are necessitated in order to comply with the rules
rather than because of changes in our ideas of classification. Examples of these
changes are the use of Agaricus rather than Psalliota, Volvariella rather than
Volvaria, and Lepiota molybdites rather than L. morgani for the green-spored
Lepiota. Such changes are regretted but only by careful adherence to the rules
and the acceptance of changes necessitated thereby, will we eventually attain a
stable nomenclature.
CLASSIFICATION
Fungi, the class of plants to which mushrooms belong, may be defined in
a general way as plants lacking true leaves, stems, and roots, lacking chlorophyll,
and reproducing by spores. They are usually divided into four main
subclasses.
The first of these is called the Phycomycetes. The fungi referred to this
group are characterized in general by the absence of cross walls or septa in the
hyphae composing the mycehum and by the production of spores within a
sac, usually a more or less swollen cell, termed a sporangium. The Phycomy-
cetes include forms such as the common bread mold, the potato-bhght fungus,
the downy mildews, many aquatic fungi and many minute, one-celled forms.
None of the Phycomycetes will be discussed in this book.
The second subclass is called the Ascomycetes. In this group the hyphae
have cross walls and the spores are produced in a speciahzed cell called an
ascus (Figure 41, p. 9). The production of spores in the ascus is regarded as a
sexual process. In the young ascus two nuclei fuse and then typically divide
three times, forming eight spores which are forcibly discharged when they are
mature. The asci may be produced directly on the mycehum or developed
within more or less speciahzed fruiting bodies. Those Ascomycetes in which
the fruiting bodies bearing the asci are structures that are closed, or that open
by a narrow pore or beak, are known as Pyrenomycetes (Figure 44, p. 9);
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