PDF - CES (IISc)

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MORPHOLOGY
In the genus Cladonia, differentiation of the generative hyphae may
observed, in CL caespiticia, a
take place at a very early stage. Wainio 1
trichogyne in a still solid podetium only 90 /x in height; usually they appear
later, and, where scyphi are formed, the carpogonium often arises at the
edge of the scyphus. Baur 2 and Wolff3 have furnished conclusive evidence
of the late appearance of the carpogonium in CL pyxidata, Cl. degenerans,
CL furcata and CL gracilis: in all of these species carpogonia with trichogynes
were observed on the edge of well-developed scyphi. Baur draws the
conclusion that the podetium is merely a vertical thallus, citing as additional
evidence that it also bears the spermogonia (or pycnidia), though at the
same time he allows that the apothecium may have played an important part
in its phylogenetic development. He agrees also with the account of the
first appearance of the podetium as described by Krabbe, who found that
it began with the hyphae of the gonidial zone branching upwards in a quite
normal manner, only that there were more of them, and that they finally
pierced the cortex. Krabbe also asserted that in the early stages the podetia
were without gonidia and that these arrived later from the open as colonists,
in this contradicting Wainio's statement that gonidia were carried up from
the primary thallus.
It seems probable that the podetium as Wainio and Baur both have
stated is homologous with the apothecial stalk, though in most cases it is
completely transformed into a vertical thallus. If the view of their formation
from the gonidial zone is accepted, then they differ widely in origin from
normal branches in which the tissues of the main axis are repeated in the
secondary structures, whereas in this vertical thallus, hyphae from the
gonidial zone alone take part in the development. It must be admitted
that Baur's view of the podetium as essentially thalline seems to be strengthened
by the formation of podetia at the centre of the scyphus, as "in CL
verticillata, which are new structures and are not an elongation of the
original conceptacular tissue. It can however equally be argued that the
acquired thalline character is complete and, therefore, includes the possibility
of giving rise to new podetia.
The relegation of the carpogonium to a position far removed from the
base or primordium of the apothecium need not necessarily interfere with
the conception of the primordial tissue as homologous with the conceptacle;
but more research is needed, as Baur dealt only with one species, CLpyxidata,
and Gertrude Wolff confined her attention to the carpogonial stages at the
edge of the scyphus.
The Cladoniae require light, and inhabit by preference open moorlands,
naked clay walls, borders of ditches, exposed sand-dunes, etc. Those with
large and persistent squamules can live in arid situations, probably because
1 Wainio 1897.
2 Baur 1904.
3 Wolff 1905.