THE BRYOFHYTA OF ICELAND 497 



cortex in this species consists of 3 4 layers of sharply defined, small 

 stereids covered with a sphagnoid outer cortex, while P. fonlana has not 

 a sharply differentiated cortical layer. This feature appears, however, 

 to be closely connected with the degree of dampness of the habitat, so 

 that forms from a dry substratum, both of P. tomentella and of P. fon- 

 tana, have several layers of thick-walled cortical cells, while bog-forms 

 have thin-walled cortical cells, and (as in Dicramim scoparium and D. 

 angnstiim] all possible transitions may be found between thin-walled and 

 thick-walled cortical cells. 



Fruit occurs very frequently and ripens at the end of July or in 

 the beinnin of Auust. 



FAM. TIMMIACE.E. 

 192. Timmia norvegica Zett. 



E. Iceland: Hof!; Vallanes (H. J.)!. N. Iceland: Pollar (St.)!; Akureyri!, 

 at an altitude of 300 metres; Hof near Evjafiordur O. D.)!; Vidimvri 



*/ *f u * 



(Grl.)!. S. Iceland: Vestmannaey!. 



It grows on earth and in rock-clefts, but has been collected every- 

 where only scantily. Near Hof (E. Iceland) it grew on gravelly ground 

 in association with Oncophoms virens, Ditrichnm flexicaule, Myurella 

 jnlacea and M. apiculata at an altitude of about 150 metres. Near 

 Akureyri it was found sometimes in rock-clefts, in company with Mniiim 

 orthorrhynchum, sometimes on rocks mixed with Philonotis tomentella. 

 Only sterile specimens have been found. 



193. Timmia austriaca Hedw. 



Very common especially in N. and E. Iceland, but more rare in 

 NW. Iceland (Dyrafjordur, Isafjordur, Grunnavik!). It grows on earth 

 or on soil-covered rocks, and often in masses. Thus in several places 

 in Hallormstadaskogur it was the most abundant member of the moss- 

 carpet under the birches, especially on knolls and soil-covered stones. 

 In several places in N. Iceland, for instance in Oxnadalur, it covered 

 the slopes along streams, often greatly mixed with other species. 



Timmia austriaca is most frequent in the lowlands up to a height 

 of about 300400 metres, but is also often found on mountain heights 

 (for instance on Seljaland at an altitude of about 620 metres) although 

 usually in small quantity. Fruit has been found only near Tvera and 

 Vidimvri in N. Iceland; it occurred plentifully in both places and had 

 just ripened at the end of July. 



FAM. POLYTRICHACE^E. 

 194. Catharinea undulata (L.) Web. 



E. Iceland: Hornafjordur!; Lon!; Berufjordur!. N. Iceland: Hof near 

 Eyjafjordur (O. D.)!; Reykir near Svinavatn Grl.)!. W. Iceland : Reykja- 



