Arthur and Kern : Peridermium 



409 



Spores thick-walled, with smooth spot. 

 Peridia high and firm (0.7-1.8 mm.). 



Spores thick-walled, without smooth spot. 

 Peridial cells very large. 

 Walls equally thick. 



Spores coarsely verrucose. 



3. P. cuicolum. 



4. P. tarneum. 



Feridial cells medium large; walls medium. 



Walls equally thick. 



Spores moderately verrucose. 

 Spores coarsely verrucose. 

 Outer wall thinner than inner. 



Spores coarsely verrucose. 

 Peridium more than one cell thick. 



Peridia cylindrical, with internal filaments. 



Branch not or slightly swollen. 

 Peridia hemispherical, imperfectly filamentose. 

 Branch not or slightly swollen. 

 Spores moderately verrucose. 

 Spores coarsely verrucose. 

 Peridia hemispherical or tortuous, without filaments 

 Branch gradually swollen into a gall. 

 Spores finely verrucose. 

 Spores coarsely verrucose. 

 Branch abruptly swollen into a gall. 

 Gall globoid, lobed and irregular. 



Peridial cells angularly globoid. 

 Gall globoid, its outline regular. 



5. P. intermedium. 



6. P. Rostmpi. 



7. P. gracile. 



8. P. jilatnentosum. 



9. P. stalactiforme 

 IO. P. pyriforme . 



11. P. Harknessii. 



12. P. fits iform e. 



13. P. mexicanum 



Peridial cells globoid. 

 Peridial cells lanceolate. 



14. P. Cerebrum. 



15. P. globosum. 



Pycnia subepidermal. 



Pycnia conspicuous, on leaves. 

 Mycelium perennial. 

 Aeciospores small. 



Peridial cells scarcely imbricated. 



16. P. boreale. 



Peridial cells considerably imbricated. 17. P. coloradense. 



Mycelium annual. 



Aeciospores medium. 

 Aeciospores large. 

 Pycnia inconspicuous, on leaves. 

 Mycelium annual. 



Aeciospores with smooth line. 



Wall thick. 

 Aeciospores without smooth line 



Wall thick. 



Wall thin. 

 Pycnia subcuticular. 



Pycnia flat, on cones. 

 Pycnia slightly convex, on leaves. 

 Peridia cylindrical. 

 Peridia flattened laterally. 



18. P. con simile. 



1 9. P. decolorans 



20. P. abietinum. 



2X. P. pseudo-bahameum 

 22. P. Hohvayi. 



23. P. conorum-Piceae. 



24. P. column a re. 



25. P. ornamentale. 



