398 DIVISION III.—MODE OF LIFE OF THE FUNGI. 
filicina, and Cunningham’s! Mycoidea parasitica which with some other allied Algae 
helps to form the species of Strigula common on evergreen leaves in the tropics. 
-2, Algae which are blue-green, violet and other colours, owing to the 
presence of phycochrome, and are often united together into large bodies by 
means of their gelatinous membranes. 
(2) Nostocaceae with their cells forming filaments: Calothrix, Ag. (Schizo- 
siphon, Kg.), Seytonema, Ag. (Fig. 167, B), Lyngbya, Ag., Nostoc, Vauch. 
(Fig. 167, C), Stigonema, Ag. (Sirosiphon, Kg.). 
(5) Chroococcaceae with their cells not forming filaments: Gloeocapsa (Fig. 
167, D), Chroococcus, Aphanocapsa, Nag. 

FIG. 168. Cystococcus. a—e from the thallus of /#7- 
bricariatiliacea. g from the thallus of Sphaerophoron 
coralloides. f from the thallus of Usnea barbata. c, 
d isolated algal cells, the rest with hyphae attached to 
them. c—/ cells dividing. a—e and g magn. 390, 
J 700 times. after Schwendener. 
FIG. 169. Trentepohlia (Chroolepus umbrinum, Kg.). 
a from the thallus of Zecanactis illecebrosa, Duf. 6 from 
the thallus of Graphis scripta. Magn. 390 times, 
Section CXV.. Origin of the Lichen-thallus. If the ripe ascospore of 
the Lichen-fungus is placed on a moist substratum, it in most cases readily puts 
out germ-tubes; these may in some cases form numerous branches (see page 113), 
but they always perish after a certain time if they do not encounter suitable Algae, 
even when the germination has taken place on a substance favourable to the nutrition 
of the Lichen. 
Supposing the substratum to be favourable and the right Alga to be within reach 
(see Fig. 170), the germ-tube puts out branches on one side, which seize on the 
Alga. If the Alga consists of single isolated cells, as for instance in the Pleurococcus- 
lichens observed by Stahl, smaller branchlets are formed at the points of contact with 
an algal cell, which closely embrace it and inclose it in fresh ramifications. If the 
Alga is a compact pluricellular body, as in the Nostoc-lichens examined by Reess, 
in which the cells united together in rows are surrounded by broad gelatinous 
membranes and the protoplasmic bodies therefore are imbedded in a large quantity 
of an intermediate gelatinous substance, the hyphal branches penetrate into the jelly 
and put out branches in it which grow luxuriantly through the algal body and unite 
with the protoplasmic bodies of the cells. At the same time in all cases known to 

ca 
} Trans. Linn. Soc. London, ser. 2, I, p. 301. 
