THE SPORE SAC LICHENS 



505 





Fig. 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-sijores, l. 

 B, edge of thallus bearing four spermagone-projections, ^{'. (Luerssen.) 



Fig. 333. — Iceland moss. A spermagone-projection, cut vertically to show 

 the cavity (sp) from which dust-spores are. discharged. (Luerssen.) 



consisting entirely of hyphse 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 th.e margin. 



A singular method of reproduction very common among 



