THE BRYOPHY1 A OF ICELAND 533 



Var. serrftfus (Warnst.). 



Isafjordur!, in pools. 



In H. exannulatum the length of the leaf-cells varies according to 

 the shape of the leaf. In the most commonly occurring forms with 

 longly pointed leaves the cells are narrow, 610 times as long as broad, 

 while short-leaved forms have leaf-cells which are only 46 times as 

 long as broad var. brachydictyon (Ren.), such forms are especially met 

 with on cold, wet gravelly ground. Fruit is rather frequent, both in 

 the type and in var. purpiirascens, and ripens at the end of July. 



293. Hypnum fluitans (Dill.) L. 

 Amblystegium fluitans (L.) De Not. 



S. Iceland: Breidabolstadr (F.)!; Breidamerkursandur (Harder!. 

 N. Iceland: Blejkjuholt (St.)!; Myvatn Grl.)!. 



Monoicous forms, which may be referred to H. fluitans occur only 

 very scantily and rarely in Iceland. The numerous older records of 

 the occurrence of this species ,'Yahl, Morch, Hornemann, Gronlund, 

 etc. are, without exception, due to erroneous determinations, and all 

 the older specimens in the collections (except one) belong to H. exannu- 

 latum or H. Kneiffii. 



H. fluitans grows everywhere in pools or on inundated ground. 

 Near Blejkjuholt Stefansson has collected a very peculiar form, with 

 erect, obtuse leaves with short nerve. The cell-tissue of the leaves is 

 very loose, and the cells of the leaf-base differ only slightly from the 

 other cells. 



\ 7 ar. falcatum Schimp. (Hypnum H. Schultzii Limpr.) 

 This very characteristic form was found abundantly, and in fruit, 

 on wet boggy ground near Kaldalon in NW. Iceland. 



294. Hypnum filicinum L. 



Amblystegium filicinum (L.) De Not. 



Very common. 



In the greater part of Iceland this species is one of the most fre- 

 quent mosses on a damp substratum, especially on wet rocks, but also 

 on gravelly ground and in bogs. In most part of N. Iceland it is some- 

 what rarer, and usually occurs more scantily. In S. Iceland it often 

 covers the faces of wet tuff-rocks in enormous mats and not rarely sets 

 a great quantity of fruit. In the rest of Iceland fruit is rarer and occurs 

 most often in the large, tomentose bog-form. In S. Iceland fruit was 

 ripe in the middle of July. 



Hypnum filicinum varies exceedingly. Bog forms and forms from 

 wet gravellj 7 ground are usually densely tomentose and regularly pinnately 

 branched. Rock forms, when growing on a more dry substratum, are 

 slender and slightly branched: on wet rocks, especially on tuff, very 

 large and vigorous, often almost like Hypnum commutatum. 



