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but differs in the whitish under surface, and in being found on 

 rocks, not tree-bark. The yellow soredia also are wanting, but 

 will be found on the similar P. incurva. P. conspersa, commonest 

 of Shield Lichens, though extremely variable, is broader in its 

 parts, and the under surface, dark brown to black, will always 

 distinguish it. The ring-like habit is not confined to P. centri- 

 fuga, nor constant in it, but is strongly suggestive when present. 



Parmelia incurva. Fist Lichen. 



Found in association with P. centrifuga, and so like it in 

 general appearance as to require no separate description. The 

 chief character determining it is the presence of globular masses 

 of yellowish soredia as much as 2 mm. or more in diameter, and 

 rather like those of P. ambigua. The ring-like habit is not usu- 

 ally noticeable. Close inspection will also show that the branches 

 tend to twist about irregularly rather than radiate from a cen- 

 tral point, while the tips usually curl, some taking the form of a 

 clenched fist. It will hardly be mistaken for any lichen except P. 

 centrifuga or P. conspersa. (See comparisons under P. centri- 

 fuga.) 



Parmelia physodes. Puffed Shield Lichen. 



A frequent species on trees and occasionally rocks in the 

 highlands and the pine barrens, becoming very plentiful in the 

 Catskills. It either forms rosettes a few cm. across, or grows 

 irregularly, often intermingled with other lichens. It may rest 

 almost flat against the foothold, or with tips lifted, or, especially 

 when on twigs, may stand out 1 or 2 cm., like the species of 

 Group 4. The habit of branching is highly irregular, trunks and 

 branches usually 1 mm. or less in width, but the tips often much 

 broadened, thickened and puffed. The upper surface is smooth, 

 greenish gray, the under surface black, but shining pale brown 

 and wrinkled under the tips, which usually curl back to show 

 the color conspicuously. Other tips may break open in a form 

 suggesting vaguely a flower of the pea family, the inner surface 

 of which is covered with pale blue dust (soredia), later turning 

 white. 



Fruits are very rare, unless P. vittata is included in P. phy- 

 sodes, as it sometimes is. But the lichen is easily determined 

 without them. 



