MARINE ALGAL VEGETATION 



151 



alga? occur. The following species are common or, at least, occur 

 very socially: — 



Chantransia Alarise. 

 Rhodochorton membranaceum. 

 R. penicilliformis. 

 Ascocyclus islandicus. 

 Ectocarpus tomentosoides. 

 Litosiphon filiformis. 



Myrionema Corunnae. 

 Phaeostroma pustulosum. 

 Pylaiella litoralis. 

 Streblonema Stilophorse. 

 Acrosiphonia incurva. 

 Ulothrix flacca. 



All the remaining Ectocar pus-species which are found on the 

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

 in particular which grow very socially: Chantransia Alariaz covers 

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

 tomentosoides also grows very socially on the fronds of Laminaria 

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

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

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



Myrionema Laminaria' and Streblonema azcidioides, in addition, 

 grow as endoph) 7 tes in the Laminaria fronds. 



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

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

 on or in Laminariacea;. 



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 Lammarza-association. On the coasts of 

 Greenland (Rosenvinge, 63) the epiphytic vegetation is much 

 scarcer in the Laminaria-helt , 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 4 — 60 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 Laminaria;, 



