PDF - CES (IISc)

I 5 8
REPRODUCTION
frequently septate, especially towards the apex, and mostly slender, varying in
width from 1-4/4, though Hue describes paraphyses in Aspicilia atroviolacea
as 8-12/u, thick. They may be thread-like throughout their length, or they
may widen towards the tips which are not infrequently coloured. Small
apical cells are often abstricted and lie loose on the epithecium, giving at
times a pruinose or powdered character to the disc. In some genera there
is a profuse branching of the paraphyses to form a dense protective epithecium
over the surface of the hymenium as in the genus Arthonia.
The apothecia may be sessile and closely adnate to or even sunk in the
thallus, or they may be shortly stalked. The thalline margin shares generally
the characters of the thallus; the disc is mostly of a firm consistency and is
light or dark in colour according to genus or species ; most frequently it is
some shade of brown. Marginate apothecia, i.e. those with a thalline margin,
are often referred to as "lecanorine," that being a distinctive feature of
the genus Lecanora. In the immarginate series, with a proper margin
only, the texture may be soft and waxy, termed "biatorine" as in Biatora;
or hard and carbonaceous as in the genus Lecidea, and is then described as
"lecideine."
In the subseries Graphidineae, the apothecium has the form of a very
flat, roundish or irregular body entirely without
a margin, called an "ardella" as in Arthonia;
or more generally it is an elongate narrow
"lirella," in which the disc is a mere slit
"> between two dark-coloured proper margins.
The hypothecium of the lirellae is sometimes
much reduced and in that case the hymenium
rests directly on a thin layer above the thalline
tissue as in Graphis elegans (Fig. 89).
Lichen fruits require abundant light, and
plants growing in the shade are mostly sterile.
B
Fig. 89. Graphis elegans Ach. A,.
thallus and lirellae; B, vertical
Naturally, therefore, the reproductive bodies
, f , , , .,,
are lo be found on the best illuminated parts
section of furrowed lirella. x ca. of the thallus. In crustaceous and in most
the upper surface,
foliose forms,
wherever the light falls
they are variously situated on
most directly. In the genera
Nephromium and Nephromopsis, on the contrary, they arise on the under sur-
face, though at the extreme margin, but as the fertile lobes eventually turn
upwards the apothecia as they mature become fully exposed. In shrubby
or fruticose lichens their position is lateral on the fronds, or more frequently
at or near the tips.
b. PERITHECIA. The small closed perithecium is characteristic of the
Pyrenocarpeae which correspond with the Pyrenomycetes among fungi. It