143 



2 and 3. Section through apothecia, apothecial branches and thallus. 

 a, thecium ; b, hypothecium ; c, medullary tissue with algae ; d, semi- 

 cortical covering. 



3. a, colored portion of cortical layer; b, colorless portion; c, sperma- 

 gonium ; d, algal layer ; e, medullary layer ; f , lower cortical layer ; 

 g, algal colonies {Microcystis'). 



4. Paraphyses and spore-sac. 



5. Spores; b, indistinct septa. 



6. Algae ; b, pyrenoid bodies. 



7. Colony of Microcystis ; c, outer covering. 

 7'. Optical section of 7. 



S. a, Sterigmatum with spermatia ; b, spermatia much enlarged. 



16. Umbilicaria Hoffm. Fl. Deutsch. Crypt. 109. 1795. 



The general appearance and structure of the thallus of Umbili- 

 caria resembles that of Gyrophora. The following are the differ- 

 ences : Cilia, rhizoids and mechanical plates are wanting ; the 

 numerous caps with basal rings of hyphal tissue (pustules) assist in 

 forming the necessary mechanical support. The histology and 

 •coloration is much as in Gyrofhora. 



The apothecial patches usually differ considerably from those of 

 Gyrofhora, being smaller and consist of clusters of minute cup- 

 shaped apothecia ; instead of being sessile upon the cortical layer of 

 the thallus, this tissue enters into their formation. The individual 

 apothecia are, however, not all cup-shaped ; they may become 

 elongated, curved or convolute. 



The arrangement of the individual apothecia relative to each 

 other produces a peculiar appearance of the upper surface of the 

 apothecial patch, resembling very closely the outline of the dentine 

 in the molar of a ruminant (also the case in Gyrofhora) . The en- 

 tire apothecial tissue is more or less dark colored. 



The spores are large, multilocular, brown in color ; each spore- 

 sac contains only one. 



The range and habitat of this group is much as in the preced- 

 ing ; they are perhaps less northern. It is represented in the terri- 

 tory by about four or five species. 



Sirosifihon ■pulvinahis and a form of Microcystis occur quite fre- 

 quently upon both upper and lower surfaces of the thallus of Gyro- 

 fhora as well as Umbilicaria, and more constantly between the 

 apothecial stalks. This is evidently a case of contingent symbiosis. 



