THE SPORE-SAC LICHENS 505 
Fic. 332.—Iceland moss (see also Fig. 161). A, tip of thallus-lobe bearing 
two fruit-patches, called apothecia, and along the edge a number of 
projections, known as spermagones, which contain dust-spores, 3. 
B, edge of thallus bearing four spermagone-projections, #2. (Luerssen.) 
Fic. 333.—Iceland moss. A spermagone-projection, cut vertically to show 
the cavity (sp) from which dust-spores are discharged. (Luerssen.) 
consisting entirely of hyphe fused into a uniform tissue. 
Layers of spore-sacs arise near the tips of the thallus-lobes in 
Cetraria, and numerous projections inclosing dust-spores ap- 
pear along the margin. 
A singular method of reproduction very common among 
