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BOTANY: PRINCIPLES AND PROBLEMS 



c 



Fig. 181. — Physcia stcllaris, a lichen. A, section through an ascocarp, show- 

 ing fruiting-surface (hymenium) of asci and. sterile hairs. B, a portion of the 

 hymenium enlarged, showing two asci and several paraphyses. C, section 

 through the thallus, showing the mass of mycelial filaments and (near upper 

 surface) a group of algal cells embedded in the mycelium. 



Fig. 182. — A lichen (Parmeiia), showing the rather thin and thallus-like charac- 

 ter of the plant body and the cup-shaped sac-fruits or ascocarps. 



