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tinctly blue-gray, and dotted with very tiny, flat, white soredia. 

 P. perlata, P. perforata and their subspecies are easily distin- 

 guished by the tips, which rise usually 1 cm. or more clear of the 

 rock, and by their frequent lumpy, white soredia or black hairs 

 along the margins. P. centrifuga, found only in the north, has 

 uniformly narrow branches, with pale under surface. Species of 

 Physcia (Group 8) may be recognized by their small size, dull 

 surface, and small blackish or gray fruits, never shining. Sticfa am- 

 plissiina (Group 7) has broad parts and light red fruits, and turns 

 bright green when wet, as does Dermatocarpon aquaticiim (Group 

 12), which is of more leathery texture, with a dull gray surface. 

 These are the Papery Lichens most frequently found growing with 

 P. conspersa. 



Pannelia Borreri. Borrer Shield Lichen 



Instead of describing this fairh- common lichen, it is simpler 

 to consider only its much more plentiful variety rude eta, here 

 named as a subspecies. For P. rudccta has become so widely known 

 under that name, that to return it where it properly belongs, as a 

 variety of P. Borreri, would not help the popular comprehension 

 of lichens. There is no difference between the two, except the 

 absence in P. Borreri of the central coral-like growths so con- 

 spicuous in P. riidecta. 



Pannelia rudecta. Rough Shield Lichen 



Also called P. Borreri var. rudccta. The commonest of the 

 conspicuous rosette lichens on tree-bark, and sometimes seen on 

 rocks ; forming more or less circular patches visible at a distance 

 of many meters, along the roadside or in open woodland anywhere. 

 It often spreads 15 cm., occasionally 30 cm., covering the bark 

 almost completely without much overlapping of the parts, for the 

 lobes are flat and wide, and their edges, meeting, tend to grow 

 together, leaving few traceable trunks or older branches. The 

 center of the lichen is more ar less covered with granules and 

 coral-like growths, which may form a crust 3 or 4 mm. thick, 

 appearing thicker where the bark is lumpy. Lobes are as much as 

 1 cm. wide, rounded, but often with finely cut margins, which, 

 however, lie flat, the upper surface pale blue-gray, often with a 



