212 



essentially different ; in Solorina the spores are elliptical, two-celled, 

 and brown in color. Owing to these marked differences in the spores 

 we can not assume that Solorina is derived from Peltigera or vice 

 versa. 



The species are essentially northern in their habitat ; they occur 

 upon moss, rock and soil. 



PLATE 73. 

 Solorina crocea (L.) Ach. 



1. Portion of thallus, natural size. 



2. Section of apothecium. 



3. Section of thallus. 



4. Spore-sac and paraphyses. 



5. Spores. 



6. Algae {Dactylococcus infusionuni) . 



7. Algae {Poly 'coccus). « 



11. Nephromium Ach. Lich. Univ. 101. 1810. 



The representatives of this genus are at once recognized by the 

 fact that the apothecia occur on the lower surface of the thallus. 



The general appearance of the thallus reminds one of Solorina 

 and Peltigera; it is, however, somewhat more lobulate and more 

 rolled in and folded ; the upper surface is sometimes rugose ; in 

 thickness and consistency it closely resembles that of Peltigera. 



Upon microscopical examination we find a well developed upper 

 cortical layer without trichomatic hyphae ; the algal layer is well de- 

 fined ; in by far the majority of species the alga is Poly co ecus puncti- 

 formis, thus indicating a relationship to Peltigera. Authors, how- 

 ever, disagree as to the symbiotic alga ; some give Dactylococcus in- 

 fusionum. I find this alga only in JV. arcticum, which should, there- 

 fore, be excluded from Nefhromium and classified under the genus 

 Ne-phroma; for the time being I have, however, refrained from 

 reestablishing this genus. If, after a careful study of these groups, 

 it is found that these algal differences apply to a number of species, 

 it will no doubt be advisable to separate them. 



The medullary layer is well developed and closely similar to that 

 of Peltigera; there is a distinct lower cortical layer, from the lower 

 surface of which the rhizoids extend. As a rule the lower cortical 

 layer is much thinner than the upper part but essentially the same in 

 structure. 



