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REPRODUCTION IN DISCOLICHENS 167
(2) The trichogynes, when present, travel up through the gonidial and
cortical regions of the thallus; Darbishire 1 observes that in Physcia pulveru-
lenta, they may diverge to the side to secure an easier course between the
groups of algae. They emerge above the surface to a distance of about 1 5/i
or less; after an interval they collapse and disappear. Their cells, which are
longer and narrower than those of the ascogonium, are uninucleate and vary
in number according to species or to individual lichens. Baur 2
thought that
possibly several trichogynes in succession might arise from one ascogonium.
(3) How many carpogonia share in the development of the apothecium
is still a debated question. In Collema only one is
functional. Baur 3 was unable to decide if one or
more were fertilized in Parmelia acetabulum, and
in Usnea Nienburg 4 found that, out of several, one
alone survived (Fig. 95). But in Anaptychia ciliaris
and in Lecanora subfusca Baur 3 considers it proved
that several share in the formation of the apothecium.
In this connection it is interesting to note that,
according to Harper 5 and others, several ascogonia
enter into one Pyronema fruit.
(4) The ascogonial cells, before and after fertilization,
are distinguished from the F
surrounding 'g; 95-
~
Vsneabarbata\jl&>.
Carpogonium with trichohyphae
by a reaction to various stains, which is dif- gynex uoo (after Nien-
bur
ferent from that of the vegetative hyphae, and s)-
also
by the shortness and width of their cells. The whole of the apothecial primordium
is generally recognizable by the clear shining appearance of the cells.
(5) *The ascogonia do not always form a distinct spiral; frequently they
lie in irregular groups. Each cell is uninucleate and may ultimately produce
ascogenous hyphae, though in Anaptychia Baur 3 noted that some of the
cells failed to develop.
(6) The hyphae from the ascogonial cells spread out in a complex layer
at the base of the hymenium, and send up branches which form the asci,
either, as in most Ascomycetes, from the penultimate cell of the fertile branch,
or from the last cell, as in Sphyridium (Baeomyces rufus)* and in Baeomyces
roseus. The same variation has been observed in fungi in a species of
Peziza 6
, in which it is the end-cell of the branch that becomes the mother-
cell of the ascus; but this deviation from the normal is evidently of rare
occurrence either in lichens or fungi.
d. HYPOTHECIUM AND PARAPHYSES. The hypothecium is the layer of
hyphae that subtends the hymenium, and is formed from the complex of
1 Darbishire 1900.
5
Harper 1900.
2 Baur 1901.
3 Baur 1904.
6 Guilliermond 1904, p. .60.
4
Nienburg 1908.