PDF - CES (IISc)

STRUCTURES PECULIAR TO LICHENS 133
2. CEPHALODIA
A. HISTORICAL AND DESCRIPTIVE
The term "
cephalodium" was first used 1
by Acharius to designate certain
globose apothecia (pycnidia). At a later date he applied it to the
peculiar outgrowths that grow on the thallus of Peltigera aphthosa, already
described by earlier writers, along with other similar structures, as " cor-
puscula," " maculae," etc. The term is now restricted to those purely vegetative
gall-like growths which are in organic connection with the thallus of
the lichen, but which contain one or more algae of a different type from the
one present in the gonidial zone. They are mostly rather small structures,
and they take various forms according to the lichen species on which they
occur. They are only found on thalli in which the gonidia are bright-green
algae (Chlorophyceae) and, with a few exceptions, they contain only blue-
green (Myxophyceae). Cephalodia with bright-green algae were found by
Hue 2 on two Parmeliae from Chili, in addition to the usual blue-green forms;
the one contained Urococcus, the other Gloeocystis. Several with both types
of algae were detected also by Hue 2 within the thallus of Aspicilia spp.
Florke 3 in his account of German lichens described the cephalodia that
grow on the podetia of Stereocaulon as fungoid bodies, "corpuscula fungosa."
Wallroth 4 who had made a , special study of lichen gonidia, finally established
that the distinguishing feature of the cephalodia was their gonidia which
differed in colour from those of the normal gonidial zone. He considered
that the outgrowths were a result of changes that had arisen in the epidermal
tissues of the lichens, and, to avoid using a name of mixed import such as
"
cephalodia," he proposed a new "
designation, calling them phymata " or
warts.
Further descriptions of cephalodia were given by Th. M. Fries 5 in his
Monograph of Stereocaulon and Pilophorus\ but the greatest advance in
the exact knowledge of these bodies is due to Forssell 6 who made a com-
prehensive examination of the various types, examples of which occurred,
he found, in connection with about TOO different lichens. Though fairly
constant for the different species, they are not universally so, and are some-
times very rare even when present, and then difficult to find. A striking
instance of variability in their occurrence is recorded for Ricasolia amplissima
(Lobaria laciniatd) (Fig. 76). The cephalodia of that species are
prominent upright branching structures which grow in crowded tufts irregu-
larly scattered over the surface. They are an unfailing and conspicuous
specific character of the lichens in Europe, but are entirely wanting in North
American specimens.
1 Acharius 1803.
4 Wallroth 1825, p. 678.
2 Hue 1904 and 1910.
5 Th. M. Fries 1858.
3 Florke 1815, IV. p. 15.
6 Forssell 1884.