— 347 — 



the frond, having up to 20 « long diameter parahel with the longitudinal 

 axis of the frond. Specimens with compressed frond constricted at inter- 

 vals also occur. The Icelandic plants are unbranched or somewhat pro- 

 liferous. 



The f. compressa grows in the upper part of the litoral region on 

 stones and rocks or in tide-pools and is rarely met with near low-water 

 mark. Fructiferous specimens have been gathered in April-— Sept. 



F. compressa is connected with f. genuina, f. minima and f. prolifera 

 by numerous intermediate forms, 



f. minima (Naeg.) Rosenv. 1. c. p. 959 ; Enteromorpha minima Stromf. 

 Algveg. p. 53, 



The specimens I have referred to this form are unbranched or some- 

 what proliferous, up to 5 cm. high, 1 mm. broad and 10 — 19 fji thick. 

 The outer and the inner walls are usually of the same thickness varying 

 from 1,5 — 3fi, but specimens with thicker walls also occur especially in 

 places in considerable distance above high-water mark. The thickness of 

 the walls of these specimens amounts io 1 /j. and both walls are, as a 

 rule, of the same thickness, but I have also sometimes seen one wall 

 thicker, and sometimes the other. Such specimens remind one highly of 

 f. micrococca. The cells in the transverse section are usually somewhat 

 higher (4 — 7 fj) than they are broad (4 — 6 fjt), but sometimes they are 

 nearly quadratic. The diameter of the cells, seen from the surface, is 

 usually 3 — 6/i long and more seldom 7 — 8//. The cells are for the 

 most part four- or five-sided or rounded. 



The typical f. minima (o: the thinwalled specimens) is closest con- 

 nected with f, compressa and there is no distinct Hmit to be drawn 

 between them; the thickwalled specimens show on the other hand the 

 transition to f, micrococca as Borgesen (1, c.) points out. 



The f. minima grows on stones and rocks at high-water mark and 

 sometimes far above it. Fructiferous specimens have been gathered in 

 June, 



f. prolifera (0. F. Mi^iller) Borgesen Fser, alg, p. 490 ; Enteromorpha 

 prolifera Rosenv. Grl. Havalg. p. 960. 



The specimens I have referred to this form are usually very prolife- 

 rous and rather large. Some of my specimens, attaining a length of up 

 to 50 cm,, are only fragments of larger plants. The main axis of my 

 plants in dry condition sometimes attains a breadth of 2 cm. The pro- 

 liferations, or branches of first order attain a length of up to 30 cm. and 

 are often densely covered on the whole surface with short, irregularly 

 placed proliferations of second order. I have also met with some speci- 



