PDF - CES (IISc)

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REPRODUCTION
apogamous genera by Metzger 1 and his work was confirmed and amplified
by Baur 2 : certain hyphae of the gonidial zone branch out into larger asco-
gonial cells which increase by active intercalary growth, by division and by
branching, and so gradually give rise to the ascogenous hyphae and finally
to the asci. Baur looked on this and other similar formations as instances
of degeneration from the normal carpogonial type of development. Moreau 3
(Fernand and Mme) have also examined Solorina with much the same
results: the paraphyses rise first from cells that have been produced by the
gonidial hyphae; later, ascogenous hyphae are formed and spread horizontally
at the base of the paraphyses, finally giving rise at their tips to the asci.
Metzger 1 had further discovered that spermogonia were absent and tricho-
gynes undeveloped in two very different crustaceous lichens, Acarospora
(Lecanora) glaucocarpa and Verrucaria calciseda, the latter a pyrenocarpous
species and, as the name implies, found only on limestone.
Krabbe 4 had noted the absence of any fertilization process in Gyrophora
vellea. At a later date, Gyrophora cylindrica was made the subject of exact
research by Lindau 5 . In that species the spermogonia (or pycnidia) are
situated on the outer edge of the thallus lobes; a few millimetres nearer the
centre appear the primordia of the apothecia, at first without any external
indication of their presence. The initial coil which arises on the lower side
of the gonidial zone consists of thickly wefted hyphae with short cells, slightly
thicker than those of the thallus. It was difficult to establish their connec-
tion with the underlying medullary hyphae since these very soon change to a
brown plectenchyma. From about the middle of the ascogonial coil there
rises a bundle of parallel stoutish hyphae which traverse the gonidial zone
and the cortex and slightly overtop the surface. They are genetically con-
nected at the base with the more or less spirally coiled hyphae, and are similar
to the trichogynes described in other lichens. Lindau did not find that they
had any sexual significance, and ascribed to them the mechanical function of
terebrators or borers. The correctness of his deductions has been disputed by
various workers: Baur 2 looks on these "trichogynes" as the first paraphyses.
The reproductive organs in Stereocaulon were examined by G. Wolff 6 and
,
the absence of trichogynes was proved, though spermogonia were not wanting.
She also failed to find any evidence of fertilization in Xanthoria parietina,
in which lichen the ascogenous hyphae branch out from an ascogonium that
does not form a trichogyne.
Rosendahl 7
, as already stated, could find no trichogynes in Parmelia
glabra. In Parmelia obscurata, on the contrary, Bitter 8 found that carpogonia
with trichogynes were abundant and spermogonia very rare. In other species
of the subgenus, Hypogymnia, he has pointed out that apothecia are either
1
2
Metzger 1903. Baur 1904.
6 Wolff 1905.
3 Moreau 1916.
7 Rosendahl 1907.
4 Krabbe 1882. 5 Lindau 1899.
8 Bitter i9oi 2 .