THE BRYOPHYTA OF ICELAND 445 



31. Dicranum fuscescens Turn. 



Iceland (Wiinstedt, deterniined by Berggren as D. Scottianum). NW. 

 Iceland: very comrnon!. W. Iceland: Nordredalur!. 



In NW. Iceland D. fuscescens is the most frequently occurring species 

 of this genus and is very conimon from the bottom of the valley up to 

 a height of 400—500 metres. It is most widely distributed from 

 about 100 to 300 metres on somewhat damp slopes covered with Vac- 

 cininin-Enipetrnm hcath, where it often constitutes the bulk of the 

 Bryoi)hyte vegetation in association with D. molle , D. scoparium and 

 occasionally, D. majiis. It is also common on the top of knoils in bogs. 

 The densely matted tufts, which are as much as 10 cm. high, are al- 

 most always interwoven with Hepaticæ, especially Lophozia spp., Ce- 

 phalozia pleniceps, C. biciispidata and Plilidium ciliare. In Nordredal it 

 was growing in birch coppices in company with Hylocomium spp. 



The fruit, which occurs rather frequently, was quite green even in 

 the beginning of July. 



All the Iceland specimens differ from the typical form and, more 

 or less, especially approach Dicranum congestum without, however, form- 

 ing any real transitional form to the latter. As a rule the leaf-nerve 

 occupies about ^/é the width of the leaf-base, but occasionally ^/s— Ve 

 only. The cells of the leaf-apex are usually quadrate or roundish, 

 mixed with numerous ones that are irregular in form; rarely, in the 

 main. shortly rectangular, in which feature it approaches var. angiisti- 

 folium Arn. et Jensen; most frequently arranged more or less distinctly 

 in rows; papillose at back, more rarely almost smooth. but in the same 

 tuft or even on the same stem rather considerable variations occur as 

 regards the development of the cell-tissue and the papillæ of the leaves. 



32. Dicranum congestum Brid. 



Very common in E. and N. Iceland and probably also in W. Iceland, 

 somewhat rarer in S. Iceland. It appears to be quite absent from 

 NW. Iceland and to be replaced there by D. fuscescens. 



It grows both on a dry and on a somewhat damp substratum, on 

 earth and humus-covered stony slopes and on the top of knoils in bogs, 

 and extends as far upwards as to the snow-line, for instance near 

 Akureyri up to about 900 melres above sea-level. In S. Iceland it has 

 not been found in the low land, but plentifully in several piaces on 

 the rocky flat, for instance near Barkastadr, 500 metres above sea-level. 



Var. subspaflicetim Arn. et Jensen occasionally occurs in localities 

 similar to those of the type, but transitional forms are of more frequent 

 occurrence. 



Nar. flejikaHle (Brid.) Br. eur. N. Iceland: Ljosavatn!. in Belnla-nana 

 heath; Hof (O. D. !. 



Only sterile specimens have been found. 



Dicranum congestum is so variable a species that it is hardly pos- 

 sible to find two piants which are exactly alike. The nerve occupies 

 Ve— Vio the Width of the leaf at its base, usually ^/8— ^9. The leaf-cells 



