Introduction to Fungi, Third Edition

520 HOMOBASIDIOMYCETES
basidiocarp become interwoven and often tightly
packed, making up the plectenchyma. If the
hyphae are less tightly packed, the resulting
tissue is known as pseudoparenchyma. Although
a range of cell types can be distinguished in the
mature basidiocarp, they all develop from
generative hyphae. Enlargement and differentiation
of basidiocarps is associated with inflation
of segments of these hyphae. Details of the
morphogenesis of basidiocarps will be described
later for selected genera.
Several kinds of development have been
described, relating to whether or not the
hymenophore is at all times exposed or is at
first surrounded by other tissues. For example,
young fruit bodies may be enveloped by a
universal veil which is broken as the pileus
expands, leaving a cup-like volva at the base of
the stipe and broken scales on the cap as in
Amanita. In some agarics the hymenophore is
protected during development by a partial veil
stretching from the edge of the cap to the stem.
Where the partial veil is thin and cobweb-like as
in Cortinarius it is termed the cortina, but where
it is composed of firmer tissues it persists as a
ring (annulus) on the stem. Agaric fruit bodies
may thus have both universal and partial veils
(Fig. 19.5), either, or neither. These different
kinds of development have been distinguished by
technical terms as follows (Reijnders, 1963, 1986;
Moore, 1998).
Gymnocarpic hymenophores are naked from
the time of their first appearance and are never
enclosed by tissue. The pileus develops at the
tip of the stipe and the hymenophore differentiates
on the lower side. Gymnocarpic development
is found in several unrelated genera, e.g.
Cantharellus, Boletus, Russula, Lactarius and Clitocybe
(Fig. 19.6a).
The angiocarpic hymenophore is enclosed by
tissue during part of its development. There are
two kinds of angiocarpic development. In primary
angiocarpy, the pileus margin, hymenophore
and sometimes also pileus and stipe
differentiate beneath the surface of the primary
tissue of the primordium (protenchyma).
Stropharia semiglobata and Amanita rubescens are
primarily angiocarpic (Figs. 19.6c,d). In a fruit
body showing secondary angiocarpy, hyphae
from an already differentiated surface grow out
towards the exterior to enclose the primordium
or part of it. The hyphae may extend from the
margin of the pileus towards the stipe, or from
the stipe to the pileus, or both. In Lentinus tigrinus
hyphae from both the pileus margin and the
stipe extend to enclose the developing gills
(Fig. 19.6b).
The tissue of the monomitic agaric-type
basidiocarp is plectenchymatous or pseudoparenchymatous.
The fruit body expands due to
inflation of the cells. Although differentiation
into skeletal or binding hyphae is limited
Fig19.5 Schematic drawing of an
agaric-type fruit body showing both
the universal and partial veils. (a) The
button stage. (b) Fully expanded fruit
body. Remnants of the universal veil
are seen as cap scales and the volva,
whereasthepartialveilhasformeda
ring (annulus) around the stipe.