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resemble P. saxatiUs. P. tiliacea will usually fruit when larger 

 than 5 cm. across, and is then more easily distinguished from 

 P. saxatilis, which seldom fruits. 



These two species may also grow on rocks, where they some- 

 what resemble the more common P. conspersa, which has a yellow- 

 ish tint, and an under surface usually brown, with comparatively 

 few holdfasts. 



P. perlata, P. perforata, and their subspecies are distinguished 

 by the larger size of their parts, and the tendency of their tips to 

 lift away from the foothold. P. rudecta and P. Borreri, also larger, 

 have the upper surface dotted with tiny white soredia, and the 

 under surface drab, with few holdfasts. 



Parmelia tiliacea var. sitblaevigata 



Also called P. sublaevigata. A variety or subspecies hardly dis- 

 tinct from P. tiliacea, but mentioned and illustrated to show the 

 limits to which the species may vary. It radiates in flat, regularly 

 branching trunks reaching a length of 4 or 5 cm. without much 

 overlapping or intermingling. Sometimes it resembles P. saxatilis, 

 but lacks the net-like pattern on the upper surface. 



Parmelia tiliacea var. isidioidea 



A name sometimes given to a rather common and often large 

 form of the species, growing on trees and rocks especially in 

 western New Jersey. Though typical P. tiliacea has no soredia, 

 granules, or coral-like growths, this variety has the shorter lobes 

 and more central parts humped up. and bearing on their summits 

 crowded hollow warts about 0.2 mm. across, often opening crater- 

 like, or again breaking down in pale, powdery soredia. Fruits are 

 rare. This variety approaches P. Borreri, but the soredia are closely 

 clustered instead of scattered, are distinctly wart-like instead of 

 flat, and the black under surface is covered with black holdfasts. 

 Or it might be taken for a small form of F. capcrata, which often 

 has similar sorediate warts on its ridges, but the blue-gray color 

 is wholly unlike the pale yellow of P. capcrata, which also has few 

 holdfasts. However, it is one of the most puzzling forms of this 

 difficult group, and different opinions may well be held regarding it. 



