THE BRYOPHYTA OF ICELAND 



503 



a a a a b b b 



Fig. 10. Polijtrichnm sexangiilare Floercke var. tencUnni. 

 a. in a damp, and b, in a dry condition (X 6). 



In lava clefts near Thingvellir and in deep lava clefts on Reykjarheidi 

 (at an altitude of about 250 metres) it was found abundantly in several 

 places in association with several other Alpine species, for instance 

 Gymnomitrium concinnalum, G. varians, Pleuroclada albescens and Pohlia 

 commutata. The occurrence of this species in such localities is un- 

 doubtedly connected with the fact that there the conditions pertaining 



\ 



a 





be d 



Fig. 11. Polytrichum sc.i-cinfiiildre Floercke var. IcncUiun. 

 a. b and c. leaves (X 15): (/. loaf-apex (X lOOj. 



