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Fruits when present are usually small, but occasionally 

 reach 7 mm. diameter, chestnut-brown or blackish, with a wavy 

 or warty rim. They will seldom be seen except on high moun- 

 tains. Spores undivided, colorless, 7 to 16 by 5 to 10 microns. 



The rich brown shades differentiate P. olivacea from most 

 other Shield Lichens that grow on tree-bark, while the smooth, 

 flat margins contrast with the toothed and raised edges of 

 Cetraria Fendleri. From the papery species of Collema (Group 

 11), which often grow on trees, its shining and hard-looking 

 surface separates it easily, for their surfaces are dull when dry, 

 gelatinous when wet. The gelatinous lichens are found usually 

 near the base of the tree, while Parmelia olivacea more often 

 occurs 1 to 3 meters high on the trunk. Dermatocarpon arboreum 

 (Group 12) is thick, dull, and when wet, bright green. Physcia 

 aquila, though brownish, has conspicuously long, narrow 

 branches and tips, overlapping shingle-fashion. 



Several varieties and subspecies of doubtful value have been 

 separated from Parmelia olivacea, and may be noted if desired. 

 P. aspidota, the most common and best justified, has the surface 

 much roughened with small warts and larger blisters, while the 

 fruit-rims are often fantastically contorted and lobed. P. con- 

 spurcata, somewhat larger, with much broader lobes, has many 

 white soredia, and whitish coral-like growths. P. prolixa, found 

 on rocks instead of trees, has narrower parts, approaching the 

 northern P. stygia. 



(Group 6 will contain all of the larger Parmelias.) 



RiDGEWOOD, N. J. 



