MARINE ALGAL VEGETATION 151 



algse occur. The following species are common or, at least, occur 

 very socially: 



Chantransia Alarise. Myrionema Corunnse. 



Rhodochorton memhranaceum. Phseostroma pustulosum. 



R. penicilliformis. Pylaiella litoralis. 



Ascocyclus islandicus. Streblonema Stilophorae. 



Ectocarpus tomentosoides. Acrosiphonia incurva. 



Litosiphon filiformis. Ulothrix flacca. 



All the remaining Ectocarpiis-species which are found on the 

 stipes occur in addition. Of the species mentioned there are three 

 in particular which grow very socially: Chantransia Alarice covers 

 the entire frond of Alaria esculenta from tip to base; Ectocarpus 

 tomentosoides also grows very socially on the fronds of Laminaria 



*/ \f 



hyperborea and L. digitata which it frequently, entirely or nearly, 

 covers during spring-time, at which time, also, Litosiphon filiformis 

 often covers large portions of the lamina of L. saccharina. 



Myrionema Laminaric? and Streblonema wcidioides, in addition, 

 grow as endophytes in the Laminaria fronds. 



Thus, at least 62 species of marine alga3, or about 59 % of the 

 algal species (113) which grow below the limit of low-tide, occur 

 on or in Laminariacece. 



On other coasts, those of the Faeroes, for example (Borgesen, 

 11 and 12), and those of Norway (Boye, 10) a similar epiphytic 

 vegetation occurs in the La/nmar/a-association. On the coasts of 

 Greenland (Rosenvinge, 63) the epiphytic vegetation is much 

 scarcer in the La/nz/?arza-belt, which is possibly due, in part, to 

 the absence of Laminaria hyperborea from that country. 



15. The Desmarestia-association. 



Desmarestia aculeata is very common and grows both scattered 

 and socially; vertically it is widely distributed, as it has been found 

 at depths of from 460 metres (in E. Iceland). It seems to grow 

 most luxuriantly at a depth of about 6 30 metres, and then is 

 frequently found in associations of lesser extent. Only rarely is 

 this association found dominant on the bottom, and even then only 

 in small patches. Most frequently it occurs intermingled with other 

 associations; thus, when dredging on a Laminaria bottom, it 

 very frequently happens that Desmarestia aculeata is brought up, 

 and as frequently as not it is intermingled with the associations 

 which extend deeper down. It often grows among the Laminarice, 



