View A43-1112-1979-eng.pdf

EDIBLE AND POISONOUS MUSHROOMS OF CANADA
circular but may vary from being somewhat irregular to fan-shaped or ear-
shaped, or sometimes shelf-like. The lamellae radiate from the stipe to the
margin of the pileus and may vary from their typical form as one or more
series of knife-blade-like structures to scarcely more than slight folds on the
under surface of the pileus.
In some mushrooms the young plant is at first completely enclosed in a
sheath of tissue called the universal veil or volva. As growth proceeds, the
volva is torn open and the young mushroom emerges, leaving remnants of the
volva as a sheath surrounding the base of the stipe. This universal veil or volva
is not present in all mushrooms but is an important character to look for in
recognizing the dangerous genus Amanita. Two types of volva are found in
Amanita. In one type, such as is found in A. virosa, the volva tears across the
top and remains as a loose, cup-like sheath around the base of the stipe. In the
other type, as in A. muscaria, the sheath is not loose but more or less grows
together with the rest of the tissue of the fruit body. As the fruit body grows,
the volva tears around the margin of the pileus rather than across the top.
Part is left adhering to the surface of the pileus where it becomes torn into
patches as the pileus expands, and part remains attached to the base of the
stipe where it may form a series of rings or patches on the stipe or form a
boot-hke cup closely adhering to the base. This second type of volva is more
difficult to recognize in the field and careful examination should be made to
determine whether or not it is present.
In some kinds of mushrooms the lamellae in the young stage are enclosed
by a layer of tissue that extends from the margin of the pileus to the stipe. This
tissue is known as the partial veil and it usually tears around the margin of the
pileus as the latter expands, and remains attached to the stipe where it forms a
ring or annulus. It may sometimes tear at the stipe and remain attached to the
margin of the pileus, which would then be described as appendiculate. Some
genera such as Amanita have both a universal veil and a partial veil, others such
as Agaricus may have only the partial veil, and in yet others such as Clitocybe
both the universal veil and partial veil may be absent.
The presence of a partial veil is frequently used as a character to distinguish
genera and its presence is usually indicated by the occurrence of the annulus
in the mature fruit body. Care must be taken in determining this character
because in some species the annulus is very delicate and may soon disappear.
It is advisable to examine young specimens to determine whether or not an
annulus is present.
The pileus, lamellae, stipe, volva, and annulus constitute the principal
parts of a mushroom that can be seen with the naked eye. Their variations in
form, color, texture, surface covering and so on are all important in the recog-
nition of species. Other characters can be observed only with the microscope,
and the research taxonomist is coming to place more and more reliance on
these microscopic characters both as a means of distinguishing between similar
species and also of providing characters that indicate relationships between
species or groups of species.