138 GUIDE TO THE STUDY OF LICHENS. 



hypothecium, which characterizes the genus. The spores 

 are two-celled, the cells united by a plasmic thread, 

 dark-brown. 



1. Pyxine picta. Thallus thin, membranaceous, 

 closely adnate to the substratum, indistinctly lobed 

 toward the margin, older portion of the thallus more 

 or less warty. Apothecia of medium size, discoid, ses- 

 sile. Disk dark to black, flattened. Spores dark- 

 brown, typical of the family, 18/x X 7/x. 



2. Pyxine sorediata. Thallus much branched, lobed, 

 long and of uniform width, grayish-green above, black, 

 with numerous rhizoids, below ; numerous soralia occur 

 along the upper margins of the lobes. Apothecia very 

 rare. Disk flattened or convex, dark. Spores dark- 

 brown, typical, 17/x X 7/x. 



This lichen requires further careful study. It is 

 perhaps not a Pyxine. Only scant and unsatisfactory 

 apothecia-bearing material has come to my notice. It 

 has been described as Pyxine cocoes^ Parmelia sore- 

 diata, Pyxine cocoes variety sorediata, as a Physcia, 



etc. 



4. Physcia, 



The thallus is almost crustose in a few of the lower 

 species ; otherwise it is typically foliose, much-branched 

 and extending flatly over the substratum. The color 

 is usually gray tinged with green above, with a differ- 

 ent color beneath, usually lighter, rarely dark to black, 

 much of the dark coloration being due to rhizoids. In 

 some species the margin of the thallus-lobes are lined 

 with dark cilia. Whitish soralia are also common upon 

 the thalli of many species. 



