PDF - CES (IISc)

REPRODUCTIVE ORGANS 157
size, rarely more than I cm. in diameter (Fig. 88); there is no development
in lichen fruits equal to the cup-like ascomata of the larger Pezizae. In
Fig. 88. Lecanora subfusca Ach. A, thallus and apothecia x 3 ;
B, vertical section of apothecium. a, hymenium; b, hypothecium;
c, thalline margin or amphithecium ; of, gonidia.
x 60 (after Reinke).
most cases the lichen apothecium retains its vitality as a spore-bearing
organ for a considerable period, sometimes for several years, and it is
of sterile
strengthened and protected by one or more external margins
tissue. Immediately surrounding the fertile disc there is a compact wall of
interwoven hyphae. In some of the shorter-lived soft fruits, as in Biatora,
this hyphal margin may be thin, and may gradually be pushed aside as the
disc develops and becomes convex, but generally it forms a prominent rim
round the disc and may be tough or even horny, and often hard and car-
bonaceous. This wall, which is present, to some extent, in nearly all lichens,
is described as the "proper margin." A second "thalline margin" containing
gonidia is present in many genera 1 : it is a structure peculiar to the lichen
apothecium and forms the amphithecium.
At the base of the apothecium there is a weft of light- or dark-coloured
and round the sides
hyphae called the hypothecium> which is continued up
as the parathecium merging into the "proper margin." It forms the lining
of a cup-shaped hollow which is filled by the paraphyses, which are upright
closely packed thread-like hyphae, and by the'spore-containing asci or thecae,
these together constituting the thecium or hymenium. The paraphyses
are very numerous as compared with the asci ; they are simple or branched,
1 See also p. 166.