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Fic. 309.—A lichen, Parmelia perlata (L.) Ach. 1. Plant, slightly reduced in 
size; a, apothecia; 6, lobe of thallus; c, soredial patches. The soredia are vegeta- 
tive reproductive bodies composed of both algal and fungal elements, and there- 
fore able to reproduce the lichen; the ascospores, alone, cannot do this. 2. Longi- 
tudinal section of apothecium; a, thecium; 5 and c, the two layers of the hypo- 
thecium; d, upper algal layer; e, colonies of algae distributed through the medullary 
layer; f, lower algal layer; g, lower cortical layer. 3. Cross-section of vegetative 
portion of thallus. 4. Paraphyses (sterile fungal filaments), and spore-sac (ascus), 
containing ascospores. 5. Ascospores. 6. Algal cells, surrounded by fungal 
hyphae with haustoria (absorbing branches). (Gager.) 
