PDF - CES (IISc)

REPRODUCTION
In size they vary from such minute bodies as those in Parmelia exasperata
which measure 25-35 p, in diam., up to nearly I mm. in Lobaria laetevirens.
As a rule, they range from about 150/4
to 400 across the widest fj, part, and are
Figj. 112. rree spermogonia in spmous
cilia of Cetraria islandica Ach. A, part
of frond; B, cilia, x 10.
generally rather longer than broad. They
open above by a small slit or pore called
the ostiole about 20 yu, to I oo /x wide which
is frequently dark in colour. In one in-
stance, in Icmadophila aeruginosa, Nien-
burg 1 has described a spermogonium with
a wide opening, the spermatiophores
being massed in palisade formation along
the bottom of a cup-like structure.
c. COLOUR OF SPERMOGONIA. Though
the ostiole is visible as a darker
usually
point than the surrounding tissue, spermogonia
are often difficult to locate un-
less the thallus is first wetted, when they become visible to slight magnification.
They appear as black points in many Parmeliae,Physciae,Roccellae, etc., though
even in these cases they are often brown when moistened. They are dis-
tinctly brown in some Cladoniae, in Nephromium, and in some Physciae\
orange-red or yellow
Usnea, Ramalina, Stereocaulon, etc.
in Placodium and concolorous with the thallus in
D. STRUCTURE
a. ORIGIN AND GROWTH. The spermogonia (or pycnidia) of lichens
when mature are more or less hollow structures provided with a distinct
wall or "
perithecium," sometimes only one cell thick and then not easily de-
monstrable, as in Physcia speciosa, Opegrapha vulgata, Pyrenula nitida, etc.
More generally the " perithecium " is composed of a layer of several cells
with stoutish walls which are sometimes colourless, but usually some shade
of yellow to dark-brown, with a darker ostiole. The latter, a small slit or
pore, arises by the breaking down of some of the cells at the apex. After
the expulsion of the spermatia, a new tissue is formed which completely
blocks up the empty spermogonium. In filamentous lichens such as Usnea
a dangerous local weakening of the thallus is thus avoided.
Spermogonia originate from hyphae in or near the gonidial zone. The
earliest stages have not been seen, but Moller 2 noted as the first recognizable
appearance or primordium of the "pycnidia" in cultures of Calicium
trachelinum a ball or coil of delicate yellowish-coloured hyphae. At a more
1
Nienburg roo8.
2 Moller 1887.