CARPOSPOREM. 
3^7 
dense pulvinate masses (as in Usnea, Rama/ina, E'vernia, P/jyscia, Parme/ia, Pertusaria, &c.). 
In the heteromerous thallus the soredia appear in the gonidial layer; single gonidia, or 
sometimes several together becoming woven over by branches of hyphse which cling 
Fig. 221. — A — D soredia of Usiiea barbata; A a simple sorediuni, consisting of a gonidium covered with a web of 
hyphce; -5 a soredium, in which tlie gonidium has multiplied by division; C a group of simple soredia, resulting from the 
penetration of the hypha; between the gonidia ; D, E germinating soredia ; the hyphse are forming an apex of growth, and 
the gonidia are multiplying; soredia oi Physcia parietijia ; « with an envelope of pseudo-parenchyma; 5 the envelope 
producing rhizines ; c a young thallus formed from a soredium (after Schwendener, X 500). 
closely to them and form an envelope of fibres. The gonidia divide repeatedly, and each 
daughter-cell is again woven over. This process is often repeated, the soredia accu- 
mulate in great numbers in the gonidial layer, and finally rupture the cortex. After 
Fig. 222.— Examples of various Algre which act as the gonidia of Lichens (after Dornet) ; h in all cases is the hypha of 
the Fungus, and ^ the gonidium. A, germinating s'^ax^ s oi Physcia pariethia, the hypha of which has attached itself to 
Protococa/s viridis ; B, a filament oi Scytonema invested by the hyphas of Stereocajiloii ramiilosum ; C, taken from the thallus 
of the Lichen, Physina chala-^muim ; a branch of the hypha is penetrating into a cell of the Nostoc-filament (gonidium) ; 
D, taken from the thallus oi Synalissa syp»/>/zorea, the gonidia are the Alga Gla'ocapsci ; E, from the thallus oi Cladoiiia 
fiircata, the gonidium (Protococcjis) is invested by hyphse. 
escaping in this manner, the soredia can still further multiply outside the thallus; but 
under favourable conditions either a single soredium or a mass of them grows out at once 
into a new thallus (Fig. 221). Schwendener states that in Vsnea barbata this may occur 
