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3o CONSTITUENTS OF THE LICHEN THALLUS
Parmelia acetabulum, another corticolous species, formed only a minute
thallus about 5 mm. in diameter, but entirely identical with normally growing
specimens.
(2) PLEUROCOCCUS.
Lecanora (Rinodina) sophodes, sown on rock in 1883, reached in 1886 a
diameter of 13 mm. with fully developed apothecia.
Lecanora ferruginea and L. subfusca after three years' culture formed
sterile thalli only.
Lecanora coilocarpa in four years, and L. caesio-rufa in three years formed
very small thalli without fructification.
(3) TRENTEPOHLIA (Chroolepus).
Opegrapha vulgata in two years had developed thallus and apothecia.
The control culture of the spores formed, as in nature, a considerable felt of
mycelium in the interstices of the bark, but no pycnidia or apothecia.
Graphis elegans. Only the beginning of a differentiated thallus was
obtained with this species.
T
Verrucaria muralis (?) gave in less than a year a completely developed
thallus.
Bonnier also attempted cultures with species of Collema and Ephebe, but
was unsuccessful in inducing the formation of a lichen plant.
H. HYMENIAL GONIDIA
Reference has already been made to the minute green cells which were
originally described by Nylander- as occurring in the perithecia of a few
Fyrenolichens as free gonidia, i.e. unentangled with lichen hyphae. Fuisting 3
found them in the perithecium of Polyblastia (Staurothele) catalepta at a very
early stage of its development when the perithecial tissues were newly
differentiated from those of the surrounding thallus. The gonidia enclosed
in the perithecium differed in no wise from those of the thallus: they had
become mechanically enclosed in the new tissue; and while those in the
outer compact layers died off, those in the centre of the structure, where a
hollow space arises, were subject to very active division, becoming smaller
in the process and finally filling the cavity. Winter's 4 researches on similar
lichens confirmed Fuisting's conclusions: he described them as similar to
the thalline gonidia but- lighter in colour and of smaller size, measuring
frequently only 2-3 ^ in diameter, though this size increased to about 7 yu,
when cultivated outside the perithecium.
Stahl 5
sufficiently demonstrated the importance of these gonidia in
1 Bonnier was probably experimenting with an Arthopyrenia. Verrucaria species combine with
Protococcus or according to Chodat with Coccobotrys gen. nov.
2 Nylander [858.
*
Fuisting 1868, p. 674.
* Winter 1876, p. 264.
5 Stahl 1877.