937 



observed it on Fiiglo, in a little stream about 200 M. above sea- 

 level. Borgesen refound it on Stromo, whence Lyngbye's record came. 

 According to Borgesen (1902, p. 492) the plant should be named 

 Enteromorpha intestinalis, var. prolifera. 



In addition to these few larger Algæ, there is crowd of smaller 

 forms, growing on stones and rocks in freshwater; these include 

 numerous Desmids and green Algæ, conspicuous amongst which 

 are the fdamentous forms: Ulothrix, Conferua, Microspora and Con- 

 jiigatae. 



c. The limnæ formation of the lakes. 



The rooted vegetation in the lakes is also very meagre. The 

 margins of most of the lakes are bare and gravelly, but occasionally 

 one meets a swamp-vegetation extending some distance into the 

 water. True aquatic piants occur in patches which only occupy 

 small parts of the surface or bottom. Lakes covered with vegetation 

 are almost unknown; a little pond in Skopen and one near Sand 

 were, however, almost entirely covered by Potamogeton natans. 



The bare strand is continued as a gravelly bottom for some 

 distance into the lake to a summer-depth^ of about 50 Cms.; beyond 

 this depth the bottom is generally soft and muddy. These con- 

 ditions prevail in most of the lakes and for the greater part of the 

 margin. At the lake outflow the appearance of the margin is 

 altered, for here the gently sloping gravel beach disappears and the 

 outlet is steep and rugged, through exposure of the solid rock, or from 

 the presence of a barricade of large boulders (Fig. 177). The extent 

 of these rocky margins varies in each lake, and several of the smaller 

 lakes are completely rock-bound. As a rule the submerged base of 

 the clifT shows no vegetation, but occasionally a growth of Fontina- 

 lis antipyretica or some green Algæ may be found (Compare the 

 lithophyte formation described above). 



The limnæ formation of the lakes is naturally grouped into 

 two associations according to the condition of the bottom and the 

 depth of water: 



a. The Litorella association extending from the shore to a depth 

 of about 50 Cms. 



^ The water covers the bare marginal zone during the higher surface-levels 

 of autumn and winter, and it is to this circumstance that the barrenness of the 

 beach is due; at its upper limit it is frequently sharply defined from the grass- 

 vegetation by a distinct low bank (Compare the amphibious association on p. 945). 



