39 



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. 



(a) Nostocaceae with their cells forming filaments : Calothrix, Ag. (Schizo- 

 siphon, Kg.), Scytonema, Ag. (Fig. 167, B], Lyngbya, Ag., Nostoc, Vauch. 

 (Fig. 167, C), Stigonema, Ag. (Sirosiphon. Kg.). 



(l>) Chroococcaceae with their cells not forming filaments : Gloeocapsa (Fig. 

 167, D), Chroococcus, Aphanocapsa, Nag. 



FIG. 168. Cystococfiis. ae from the thallus of Im- 

 tricaria tiliacea. g from the thallus of Sphatrophoron 

 coralloides. f from the thallus of Uinea barbata. c, 

 ri isolated algal cells, the rest with hyphae attached to 

 them, cf cells dividing, ae and g magn. 390, 

 f 700 times, f after Schwendener. 



FIG. 169. Trentepohlia (Chroolepus umbriniim. Kg. I. 

 a from the thallus of l.ecanactis illecebrosa, Duf. b from 

 the thallus of Graphis sin'fta. 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 



1 Trans. Linn Soc. London, ser. 2, 1, p. 301. 



