Encyclopedia Britannica 1963 [16].pdf

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ENCYCLOPEDIA
BRITANNICA
T H E UNIVERSITY O F CHICAGO
The Encyclopgdia Britannicd
ir
published with the editorial adpice ofthe
farzlltips
of The University
of
Chicago and ofa
committee of members ofthefaczlltiPJ
of
Oxford, Cambridge
and London universities and
of
d
committee
at The University of Toronto
*
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Volume 16
M
USHROOM
TO
O
ZONOLYSIS
ENCYCLOPEDIA BRITANNICA,
INC.
WILLIAM
BENTON,
PUBLISHER
CHICAGO
LONDON
TORONTO
GENEVA
SYDNEY
PRINTED
IN
THE
U.S.
A.
Volume
16
The well known, edible, umbrella-
shaped fungus which is grown for the market
and commonly served as a delicacy is called by
many people "the mushroom." Botanically it is
known as Agericus campestris, or by some authors
as Psalliota campestris. I n the temperate regions of the earth it
is often found growing wild, in pastures, lawns, golf courses, etc.,
where the grass is kept short and the ground is enriched by ma-
nure. Restriction of the name mushroom to this fungus alone
is not in accordance with the terminology accepted by botanists,
nor in most regions does it correspond with popular usage. Hun-
dreds of other umbrella-shaped fungi occur in nature and are to
be found in numbers unbelievable to those who have not made a
deliberate search for them. These differ from Agaricus campestris
in minor characters of form, structure, and colour. Many of them
are edible, a few are deadly poisonous, others are too tough or
unpalatable to serve as food. The botanist calls all of these mush-
rooms. Such umbrella-shaped fungi in most cases bear on the
under side of the expanded upper portion or cap (pileus) a num.
ber of flat, knife-blade shaped parts (gills) which radiate like the
spokes of a wheel from the handle or stalk (stipe) to the mar-
gin of the cap. Possession of these radiating gills marks a fungus
as a member of the family Agaricaceae, these fungi being com-
monly called "agarics." Other closely related umbrella-shaped
fungi outside this family lack gills. In the Boleti, for example,
there may be seen on the under side of the umbrella. myriads
of tiny pores which are the mouths of cylindrical tubes, while
in members of the family Hydnaceae pendent spines occur in-
stead. Still other related fungi lack the typical umbrella-shape,
and show wide variation in form. The coral fungi (Clavariaceae)
have the aspect of delicately coloured coral, and may be much
branched like a deciduous tree. Others occurring on the sides
of stumps, fallen logs, or trees are known as the bracket fungi
and have the aspect of little shelves overlapping one above the
other. The hundreds of species of all these various sorts of fungi
possess, for the most part, a soft texture or flesh and the whole
aggregation are commonly termed the "fleshy fungi." The ap-
plication of the name mushroom to all of them accords with
professional and popular usage for the most part. Some people
use the term mushroom only for the edible members of this great
USHROOM.
group, and call those which are not edible toadstools. Although
botanists recognize the word toadstool they regard it as synony-
mous with mushroom and write at times "edible toadstool" or
"poisonous mushroom." I n general they avoid the term toadstool.
The Agaricaceae, characterized as noted above, by the posses-
sion of gills on the under side of the pileus, embrace more than
fifty different genera. These constitute five groups differing in the
colour of the dust or powder which falls from the gills a t matur-
ity. This dust, composed of many thousands of tiny, unicellular
spores, which float downward in such quantity as to form a notice-
able deposit on the grass or earth beneath the fungus, may be
easily caught for examination if a sheet of paper be placed di-
rectly beneath the cap. The colour of this spore dust in some
genera is white. I n others i t is pink, purple-brown, rusty brown
or black. The group characterized by possession of purple-brown
spores contains about ten genera, one of which is Agaricus. The
well known mushroom of commerce,
A.
canzpestris, is only one of
a dozen or more species composing this genus. Some genera con-
tain many dozens of species. I n any given genus the species all
possess in common certain prominent features of form, colour or
structure which serve to distinguish them from those of other
genera. Within a genus the species differ from one another in
more minor characters of the same sort, it being necessary in
many cases to take note of microscopic points of dissimilarity.
Consideration of the genus Agaricus in this connection will serve
to illustrate this situation concretely. All the species of the
genus have purple to purple-brown spores, and the gills, which are
white when young, change gradually through pink and successive
shades of deepening brown as the spores reach maturity over their
surface. The ends of the gills nearest the stipe are not attached
to it and are not disturbed when the stipe is torn from the
pileus. On the under side of the pileus of the young opening um-
brella there is a chamois-skinlike membrane stretching from the
stipe to the margin of the pileus and hiding the gills from view.
A
little later this membrane
(veil)
detaches itself from the margin
of the pileus and falls to form a ring
(annulus)
around the stipe.
I n the other genera having purple-brown spores the gills are at-
tached to the stipe and an annulus is lacking. The characters
which serve for the identification of the genus Agaricus are thus
seen to be few and readily recognized.

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