130 H. JONSSON 



greatly in size and form and may be at times considerably elon- 

 gated, bearing then a striking resemblance to an Enteromorpha. 

 Under calm conditions the inflated stage continues until the spores 

 at the apex of the frond are ripe. 



In several places in the fjords Monostroma Grevillei var. typica 

 forms a luxuriant, characterizing vegetation at a depth of about 

 3 — 5 metres. 



Monostroma fuscum very frequently forms associations of con- 

 siderable extent in the fjords at a depth of about 4 metres. The 

 specimens of this species which occur there are generally very large 

 (f. grandis). These large specimens are rather frequently found at 

 low-water mark, detached or floating at the water's edge, and then 

 it may generally be taken for granted that a Monostrometum exists 

 further out at a depth of about 4 metres. 1 Both in the fjords of 

 E. Iceland and in Eyjafjordur in N. Iceland this Monostrometum oc- 

 curred in the same characteristic manner, viz. alternating with a 

 Chordarietum, a Dictyosiphonetum (D. foeniculaceus) , a Halosaccione- 

 tnm, and a Rhodymenietum. Generally the order was that Rhodymenia 

 grew deepest (as deep as 12 metres), and M. fuscum most frequently 

 uppermost (at about 4 metres). Alaria and Laminaria saccharina, in 

 addition, may be found growing scattered in such places, which 

 makes the character of the vegetation still more heterogeneous. 



Monostroma undulatum does not occur so abundantly as do the 

 other Monostroma species. It is found growing rather luxuriantly, 

 however, in pools in the lower littoral zone, and on the stems of 

 Laminaria in comparatively low water. 



Ulva Lactuca, also, is most nearly related to this association. 



This association is very common in the Faeroes (cf. Borgesen, 

 12, pp. 731 and 764), and occurs also in Greenland (Rosenvinge, 63). 



9. The Chorda-association. 



This association is composed of rather large, brown algae. The 

 fronds are either non-branching, thick filaments (Chorda, Scytosiphon), 

 or else branched, as in almost all the others; one, Coilodesme, how- 

 ever, is almost leaf-like. 



This association has an insignificant distribution, and is found 

 usually in patches, where the substratum is cla3 r ey or somewhat 

 muddy. It occurs both in the lower littoral zone above low-water 

 mark, and to a depth of at least 4—6 metres. The members of the 



1 Stromfelt (70, p. 11) mentions this Monostrometum at Eskifjor5ur. 



