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DISCUSSION OF LICHEN REPRODUCTION 177
absent or occur but seldom, while spermogonia are numerous, and he concludes
that the spermatia must function as spores or conidia. Baur 1 however does
not accept that conclusion; he suggests as probable that the male organs
persist longer in a functionless condition than do the apothecia.
Still more recently Nienburg 2 has described the ascogonium of Baeo-
myces sp. and also of Sphyridium byssoides (Baeomyces rufus) as reduced
and probably degenerate. His results do not disprove those obtained by
Krabbe 3 on the same lichen {Sphyridium fungiforme). The apothecia are
terminal on short stalks in that species. When the stalk is about '5 mm. in
height, sections through the tip show numerous primordia (12 to 15) ranged
below the outer cortex, though only one, or at most three, develop further.
These ascogonial groups are connected with each other by delicate filaments,
and Nienburg concluded that they were secondary products from a primary
seen in what he
group lower down in the tissue. Spirals were occasionally
considered to be the secondary ascogonia, but usually the fertile cells lie in
loose uncoiled masses; isolated hyphae were observed to travel upwards
from these cells, but they never emerged above the surface.
Usnea macrocarpa if Schulte's 4 work may be accepted is also apo-
gamous, though in Usnea barbata Nienburg 2 found trichogynes (Fig. 95)
and the various developments that are taken as evidence of fertilization.
Wainio 5 had demonstrated emergent straight trichogynes in Usnea laevis
but without any sign of fertilization.
E. DISCUSSION OF LICHEN REPRODUCTION
In Ascolichens fertilization by the fusion of nuclei in the ascogonium
is still a debated question. The female organ or carpogonium, as outlined
above, comprises a twisted or spirally coiled multiseptate hypha, with a
terminal branch regarded as a trichogyne which is also multiseptate, and
through which the nucleus of the spermatium must travel to reach the
female cell. It is instructive to compare the lichen carpogonium with that of
other plants.
a. THE TRICHOGYNE. In the Florideae, or red seaweeds, in which the
trichogyne was first described, that organ is merely a hair-like prolongation
of the egg-cell and acts as a receptive tube. It contains granular proto-
plasm but no nucleus and terminates in a shiny tip covered with mucilage.
The spermatium, unlike that of lichens, is a naked cell, and being non-motile
is conveyed by water to the tip of the trichogyne to which it adheres; the
intervening wall then breaks down and the male nucleus passes over. After
this process of fertilization a plug of mucilage cuts off the trichogyne, and
it withers away.
1 Baur 1904.
-
Xienburg 1908.
3 Krabbe 1882. 4 Schulte 1904.
5 Wainio 1890.
S. L. 12