PDF - CES (IISc)

CONSTITUENTS OF THE LICHEN THALLUS
of species and he designates the algae, according to the lichen in which
they occur, as Cystococcus Cladoniae pyxidatae, C. Cladoniae Jimbriatae, etc.
Meanwhile Paulson and Somerville Hastings 1
by their careful research
on the growing thallus have thrown considerable light on the identity of the
Protococcaceous lichen gonidium. They selected such well-known lichens
as Xanthoria parietina, Cladonia spp. and others, which they collected
during the spring months, February to April, the period
Fig. 23. Cystococcus Cladoniae
pyxidatae Chod. from culture
x 800 (after Chodat).
of most active
growth. Many of the gonidia, they found, were in a stage of reproduction,
that showed a simultaneous rounding off of the
gonidium contents into globose bodies varying in
number up to 32. Chodat had figured this method
of "sporulation" in his cultures of the lichen gonidium
both in Chlorella Beij. and in Cystococcus Chod.
(Fig. 23). It has now been abundantly proved that
this form of increase is of frequent occurrence in the
thallus itself. Chlorella has been suggested as .prob-
ably the alga forming these gonidia and recently
West has signified his acquiescence in this view 2 .
2. CHLORELLA Beij. Occurring frequently on damp ground,
'ig. 23 A. A, C, Chlorella vulgaris
Beyer. B and C, stages in division
x about 800 (after ; Chodat) E,
Chi. faginea Wille x 520 (after
Gerneck); F I Chi. miniata ; F,
vegetable cell G ; I, formation
and escape of gonidia x 1000
(after Chodat).
bark of
trees, etc., dividing into numerous daughter-
cells, probably reduced zoogonidia (Fig. 23).
Chodat distinguishes between Cystococcus
and Chlorella in that Cystococcus may form
zoospores (though rarely), Chlorella only
aplanospores. He found three gonidial species,
Chlorella lichina in Cladonia rangiferina, Ch.
viscosa and Ch. Cladoniae in other Cladonia
spp.
3. COCCOBOTRYS Chod. The cells of this
new algal genus are smaller than those of
Cystococcus oxProtococcus and have no pyrenoid.
They were isolated by Chodat from the thallus
of Verrucaria nigrescens (Fig. 24), and, as
they have thick membranes, they adhere in
a continuous layer or thallus. Chodat also
claims to have isolated a species of Cocco-
botrys from Dermatocarpon miniatum, a foliose
Pyrenolichen.
4. COCCOMYXA Schmidle. Cells ellipsoid, also without a pyrenoid.
Two species were obtained by Chodat from the thallus of Solorinae and
are recorded as Coccomyxa Solorinae croceae and C. Solorinae saccatae.
1 Paulson and Hastings 1920.
2 Paulson in litt.