PLATE V. A Common Tree Lichen (Physcia stellaris} 



A, habit sketch ; B, diagram of a section through a sac fruit (ascocarp), showing 

 the fruiting surface and layer of algal cells; C, section showing a group of 

 algal cells (Pleurococcus), held in the network of fungal filaments; I), section 

 of the fruiting surface, showing sacs (asci) in stages of development among 

 the sterile filaments (paraphyses) 



