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FUNGI
of the hymenium. In the Agaricaceae, or mushrooms, the hymenium covers
the surface of thin blades or gill-Hke structures termed lamellae which are
more or less radially arranged on the under surface of the pileus. In the Hyd-
naceae it covers the surface of tooth-like structures. In the Boletaceae the
hymenium lines the inner surface of tubes and the fruiting body is soft, fleshy,
and mushroom-like whereas in the Polyporaceae it also hnes the surface of
tubes but the fruiting body is tough, corky to leathery, or woody. In the
Clavariaceae it is smooth and covers the entire fruiting body; whereas in the
Thelephoraceae it is also smooth but the fruiting body is more or less dif-
ferentiated into an upper, sterile surface, and a lower, fertile surface.
The above brief account is an outline of the traditional basis for dis-
tingiiishing these famihes of Basidiomycetes but as a result of recent studies of
microscopic structure, chemical reactions, cultural characters and so on,
modern taxonomists are pretty generally agreed that it is not a satisfactory
classification from a scientific standpoint. For example, Lenzites has lamellae
but is obviously much more closely related to the polypores than to the other
mushrooms, and Gomphidius has lamellae but is apparently more closely
related to the boletes than to the mushrooms. Many other examples could be
given. However, for the purpose of this book the traditional classification is
quite satisfactory.
In the Gasteromycetes or puffballs, the basidia are produced in a closed
fruiting body and not arranged in a hymenium. The spores are not forcibly
discharged into the air but are disseminated by wind, rain, and insects.
Other groups of Basidiomycetes may exhibit variations in the form and
structure of the basidium itself. In the Auriculariaceae the basidium becomes
transversely septate, the cross walls forming four cells from each of which a
sterigma arises (Figure 40, p. 9). In the Tremellaceae the basidium becomes
longitudinally septate and the walls are at right angles ; consequently four cells
are formed, from each of which a sterigma arises (Figure 38, p. 9). In the
Dacrymycetaceae the basidium becomes deeply divided or forked with sterigmata
at the apices of the forks (Figure 39, p. 9).
One large group of Basidiomycetes is not discussed in this book. This
group consists of the rusts and smuts, which live as parasites on other plants
and in which the basidium has cross walls and is produced directly on germina-
tion of a speciahzed, thick-walled resting spore rather than in a fruit body.
The above classification may be presented briefly as follows
FUNGI
Phycomycetes — hyphae lacking cross walls; spores borne in sporangia
Ascomycetes — hyphae with cross walls; spores produced in asci
Plectomycetes — asci produced directly on the mycehum
Pyrenomycetes — asci produced in a closed fruiting body or perithecium
Discomycetes — asci produced in an apothecium, a fruiting body with
an exposed fruiting surface
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