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purplish iridescence when wet. There is a slight tendency toward 

 netted wrinkles as in P. saxatilis, but these are vague. Sprinkled 

 everywhere on the smooth and rather shining surface, are white 

 dots of soredia averaging perhaps 0.05 mm. in diameter, and hardly 

 visible without a lens. These may lie perfectly flat, but are usually 

 slightly raised on older parts. The under surface is smooth, pale 

 drab at the tips, sometimes darkening, and occasionally almost 

 black toward the center, where it is shaggy with drab holdfasts. 



Fruits, rarely seen except on very large specimens, are irregu- 

 larly cup-shaped, dark brown, up to 5 mm. across. Spores un- 

 divided, colorless, 10 to 16 by 6 to 9 microns. 



The central rough crust, and the pale, blue-gray color, dotted 

 with tiny, white soredia, will distinguish Parmelia rudecta from 

 all other lichens, after a little observation, and the smooth, pale 

 under, surface of the tips usually prevents confusion with P. saxa- 

 tilis var. furfuracca and P. tiliacea var. isidioidea, which are black 

 beneath. Another lichen with the central coral-like growths is 

 Cetraria aleurites (Group 5), without blue-gray color or white 

 dots. P. Borreri lacks the central crust, but the other characters 

 are identical with P. rudecta, and there is little chance for confu- 

 sion. Yet Sticta amplissima (Group 7) has found its way into 

 herbaria under the label of P. Borreri, and the differences should 

 be carefully noted. Sticta amplissima is pinkish gray or pearl-gray, 

 with plentiful light red fruits. The upper surface is smooth, or 

 stretched into wrinkles and has no white dots. The under surface 

 is clothed with a pale felt. In the field, it is only necessary to wet 

 the Sticta, which will almost immediately turn deep grass-green. 

 P. Borreri turns color hardly at all when wet, becoming somewhat 

 more blue or purplish. P. perlata is sometimes mistaken for P. Bor- 

 reri, especially as it may have small, faint dots on the upper surface. 

 The raised margins, often edged with lumpy soredia, and the black 

 under surface, chestnut-brown at the tips, should suffice to dis- 

 tinguish it. 



Pannclia capcrata. Wrinkled Shield Lichen 



A rival of P. rudecta for the frequency with which it is seen on 

 trees, and certainly without rival for showiness, whether on bark, 

 or with P. conspcrsa on lioulders. Roadside oaks are often blan- 

 keted with its pale lemon-yellow mats 30 or 40 cm. across, reach- 



