PDF - CES (IISc)

REPRODUCTION IN DISCOLICHENS
the view that there had been fertilization: the cells of the trichogynej had
lost their turgidity and at the same time the cross-walls had swollen con-
siderably and stood out like knots in the
hypha (Fig. 92). The ascogonial cells had
also increased not only in size but in number
by intercalary division, so that the spiral
arrangement became obscured. Ascogenous
hyphae arose from the ascogonial cells, and
asci cut off by a basal septum were finally
formed from these hyphae. Lateral branches
from below the septum also formed asci.
Stahl's observations were repeated and
extended by Borzi 1 on another of the Colle-
maceae, Collema nigrescens. In that plant the
foliaceous thallus is of thin texture and has
a distinct cellular cortex. The carpogonia
were found at varying depths near to the cortical
region; the ascogonium, of two and a
half to four spirals, consisted often to fifteen
cells with very thin walls, the trichogyne of
five to ten cells, the terminal cell projecting
above the thallus. Borzi also found spermatia
Fig. 92.
fused with the tip-cell.
A further important contribution was made by Baur" in his study of
Collema microphyllum Ach.
Carpogonium and trichogyne after
copulation x 500 (after Stahl).
Collema crispum*. There occur in nature two forms of this lichen, one of
them crowded with apothecia and spermogonia, the other with a more
luxuriant thallus, but with few apothecia and no spermogonia. On the latter
almost sterile form Baur found in spring and again in autumn immense
numbers of carpogonia about one thousand in a medium sized thallus
which nearly all gradually lost the characteristics of reproductive organs,
and, anastomising with other hyphae, became part of the vegetative system.
In a few cases in which, presumably, a spermatium had fused with a tricho-
gyne, very large apothecia had developed.
As the first-mentioned form was always crowded with apothecia in every
stage of development, as well as with carpogonia and it spermogonia, seemed
natural to conclude that the difference was entirely due to the presence or
absence of spermatia in sufficient numbers to ensure fertilization. The
period during which copulation is possible passes very rapidly, though
subsequent development is slow, occupying about half-a-year
of fertilization to the formation of the first ascus.
161
from the time
1
Borzi 2
1878.
Baur 1898.
3
Fiinfstiick (1902) suggests that the lichen worked at by Baur is Collema cheileuni Ach.