PDF - CES (IISc)

154
MORPHOLOGY
In Corella, the mature lichen is squamulose or consists of small lobes; in
Dictyonema there is a rather flat dimidiate expansion; in both the alga is
Scyt0nema,thetrichomes of which largely retain their form and are surrounded
by parallel growths of branching hyphae. The whole tissue is loose and
spongy.
Corella spreads over soil on a white hypothallus without rhizinae. In
the other two genera which live on soil, or more frequently on trees, there
is a rather extensive formation of hold-fast tissue. When the dimidiate
thallus grows on a rough bark, rhizoidal strands of hyphae travel over it
and penetrate between the cracks; if the bark is smooth, there is a more
continuous weft of hyphae. In both cases a spongy cushion of filamentous
tissue develops at the base of the lichen between the tree and the bracket
thallus. There is also in both genera an encrusting form which Johow
regarded as representing a distinct genus Laudatea, but which Moller found
to be merely a growth stage. Moller 1
judged from that and from other
characteristics that the same fungus enters into the composition of both
Cora and Dictyonema and that only the algal constituents are different.
C. SPORIFEROUS TISSUES
As in Hymenomycetes, the spores of Hymenolichens are exogenous,
and are borne at the tips of basidia which in these lichens are produced on
the under surface of the thallus. In Cora the fertile filaments may form a
continuous series of basidia over the surface, but generally they grow out
in separate though crowded tufts. As these tufts broaden outwards, they
tend to unite at the free edges, and may finally present a continuous
hymenial layer. Each basidium bears four sterigmata and spores (Fig. 87 e}\
paraphyses exactly similar to the basidia are abundant in the hymenium.
In Dictyonema the hymenium is less regular, but otherwise it resembles that
of Cora. No hymenium has as yet been observed in Corella; it includes, so
far as known, one species, C. brasiliensis , which spreads over soil or rocks.
1 Moller 1893.