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EDIBLE AND POISONOUS MUSHROOMS OF CANADA
When a spore germinates it puts forth a slender thread called a hypha.
This thread grows rapidly, develops cross walls or septa and becomes many-
celled, then branches repeatedly, producing a mat of hyphae termed the
mycelium. This is the vegetative part of the fungus from which the fruiting
body or mushroom arises. The mushroom is composed of hyphae consisting
of interwoven, branched, septate threads, although in some groups such as
Lactarius and Russula there are also globular cells termed sphaerocysts in the
tissue.
The structure of the lamellae is of special interest because it is here that
the spores are produced. If a section of a lamella is examined it is seen to be
roughly wedge-shaped or triangular. The spores are produced on the outer
surface in a definite layer called the hymenium whereas the central part is
composed of more or less interwoven hyphae and is called the trama (Figure
42, p. 9). The hymenium consists of basidia, paraphyses, and sometimes
cystidia. The basidia are the cells on which the spores are produced; each one
has four little stalks at its apex and a spore develops on the tip of each stalk.
Between the basidia there are cells somewhat similar in shape but lacking the
stalks and never producing spores. These are the paraphyses. Their function is
apparently to hold the basidia far enough apart that their slightly sticky spores
will not become entangled and prevented from shooting forth. In some mushrooms
there are also specialized cells of varying shape and size that project
from the hymenium and are called cystidia. They may be rounded, pointed,
thick- or thin-walled, sometimes encrusted, and variously shaped, but they are
usually constant for each species. Cystidia may also occur on the surface of the
pileus or on the stipe. Their exact function is still uncertain but when present
they can be of great assistance in the identification of the species.