Introduction to Fungi, Third Edition

SPORES OF FUNGI
27
are unicellular, but they may become septate
after release in some members of the
Heterobasidiomycetes (Chapter 21). In shape,
basidiospores are asymmetric and vary from
sub-globose, sausage-shaped, fusoid, to almondshaped
(i.e. flattened), and the wall may be
smooth or ornamented with spines, ridges or
folds. The colour of basidiospores is important
for identification. They may be colourless,
white, cream, yellowish, brown, pink, purple
or black. The spore colour may be due to pigments
in the spore cytoplasm or in the spore
wall. The appearance of pigments in the wall
occurs relatively late in spore development.
This explains the change of colour of the gill
of a domestic mushroom (Agaricus) from pink,
due to cytoplasmic spore pigments, to dark
purplish-brown when mature, due to wall
pigments.
The generalized structure of a basidiospore is
illustrated in Fig. 1.20. Most basidiospores have
a flatter adaxial face and a more curved abaxial
face. The point of attachment of the spore to the
sterigma is the hilum, which persists as a scar
at the base of a discharged spore. Close to the
hilum is a small projection, the hilar appendix.
This is involved in the unique mechanism of
basidiospore discharge, in which a drop of liquid
perched on the hilar appendix coalesces with
a second blob of liquid on the spore surface,
Fig1.20 Generalized view of a median vertical section
through a basidiospore as seen by transmission electron
microscopy.For clarity, structures such as endoplasmic
reticulum and ribosomes are not illustrated. Diagram
based on Agrocybe acericola, after Ruch and Nurtjahja
(1996).