213 



The apothecia are borne on the margin of the lower surface of the 

 lobes ; they are quite large, orbicular or transversely oval ; there is a 

 line of demarcation between thallus and apothecium which consists 

 of a slight ridge of semi-cortical tissue gradually merging into the 

 lower cortical tissue and the thecium. Although the apothecia are 

 developed on the lower surface of the thallus, the disk is turned up- 

 ward ioo° or more by a folding back of the lobe of the thallus ; this 

 movement is slowly brought about by a more rapid development of 

 the lower cortical tissue in the immediate vicinity of the apothecium. 

 The general characters of epithecium, thecium and hypothecium are 

 the same as in Peltigera. 



The spores are spindle-shaped, almost acicular in some species,, 

 tinged with a brown coloration and two to six-celled. 



The range and habitat of the Nej)hromiums seems to be about 

 the same as that of the Peltigeras. 



PLATE 74. 

 Nephromium laevigatum Ach. 



1. Natural size ; a, apothecia on upturned lobes of thallus. 



2. Section of apothecium. 



3. Section of thallus. 



4. Paraphyses and spore-sac. 



5. Spores. 



6. Spores of Nephroma arcticum. 



7. Algae {Dactylococcus infusionum) of N. arcticum. 



8. Algae {Poly coccus punctiformis) enclosed by hyphae. 



9. Free cells of 8 at a, colony at b. 



12. Stictina Nyl. Flora, 43 : 65-66. i860. 



Many authors combine this genus with Sticta, since the general 

 structural characters are the same in both genera, but the constant 

 algal differences make it more consistent to keep them separate. It 

 is in all respects a condition similar to that of Psoroma and Panna- 

 ria ; that is, Stictina represents the oldest type from which Sticta 

 branched off by a process of special algal adaptation. 



The thallus is quite large, typically foliose, of medium thickness, 

 not brittle ; lobation is usually quite distinct ; there is no marked 

 tendency in the lobes to ascend; they lie quite flat upon the sub- 

 stratum to which they are rather loosely attached by means of long 



