— 344 - 



situations in the literal region, from above high-water marlc to low-water 

 mark, but it is usually most common in the upper part of the litoral 

 region especially in the pools. 



f. genuina Rosenv. 1. c. p. 957, Stromf. Algveg. p. 52, 



The specimens, I have referred to this form, are 2 — 40 cm. high, 

 1 mm. — 1 cm. broad and 16 — 40 [i thick. The most typical specimens 

 are unbranched, and through the whole frond the inner walls of the cells 

 are considerably thicker than the outer walls. The thickness of the walls 

 is somewhat varying. In the lower part of the frond I have thus found 

 the thickness of the inner walls varying from 4 — \0 fj. and the thickness 

 of the outer walls varying from 1,5 — 7/^. The cells of the lower part 

 of the frond are in the transverse section 9 — 28^ high and 7— 14^ broad 

 and the section often fully resembles the figure given by Ahlner (Entero- 

 morpha fig. 1 h). The upper part of the frond is considerably thinner and 

 the cells lower, sometimes of a nearly quadratic shape ; the cell walls are 

 also considerably thinner than in the lower part of the frond, but the inner 

 walls are still the thickest. I have also frequently met with specimens, 

 which had a thickened inner wall only in the lower part of the frond, but 

 the inner and the outer walls of the upper part of the frond were about 

 of the same thickness and rather thin. The typical f. genuina is by inter- 

 mediate forms closely connected to f. micrococca. 



Specimens with cylindric frond, having the inner and the outer walls 

 of about the same thickness and rather thin, not rarely occur. More 

 seldom 1 have seen specimens with cylindric fronds constricted at inter- 

 vals, and occasionally 1 have met with plants having partly cylindric 

 and partly compressed fronds. Such specimens form the transition to 

 f. compressa. 



To this form 1 have also referred specimens, which were somewhat 

 branched below and sometimes furnished with short proliferations above 

 having a somewhat thickened inner wall. These specimens are to be 

 regarded as transitory forms to f. prolifera, from which they are not easily 

 distinguishable. 



At Kolbeinsa in NW. Iceland I met with some specimens with cylin- 

 dric frond, having somewhat thickened inner walls, without proliferations 

 and furnished witli trabeculae as described by Rosenvinge for Enteromor})a 

 prolifera var. trabeculata and by Borgesen for Enteromorpha intestinalis 

 var. compressa, var. prolifera and E. clathrata. As mentioned by Rosen- 

 vinge and Borgesen the trabeculae turn yellow by chlor-zinc-iodide. The 

 outermost layer of the outer wall of the frond and the innermost layer 

 of the inner wall also sometimes turn yellow by chlor-zink-iodide. 



The trabeculae turn red by ruthenium oxychloratum ammonia, and 



