THE SPORE-SAC LICHENS 



507 



mm 



Fig. 335. — Iceland moss. A small part of the apothecium and thallus shown 

 in Fig. 334, magnified 400 diameters; showing the spore-sacs or asci (a), 

 the paraphyses (p), the compact layer of mycelium (s) from which they 

 arise, the algae (Pleurococcus) known as "gonidia" (g), the cottony 

 mycelium (m), and the compact protective rind (r, r'). (Luerssen.) 



Fig. 3.36, I. — Beard-lichen (Usnea barhata. Beard-lichen Family, Usneacew). 

 Natural size. Granules often appearing on the surface are soredia. 

 (Baillon.) — Grayish or dull yellowish green throughout; often much 

 longer than shown, with a tough central. Conmion on trees in various 

 parts of the world. 



finally, keeps them supplied with all the carbon dioxid 

 they need as a raw material for their food. Dissimilar or- 

 ganisms living thus together with benefit to both are called 



