82 M. FOSLIE. [1905 



The encompassing is generally so complete and coherent, that such 

 a specimen conveys the impression of being an alga thoroughly 

 independently developed, now strongly branching, now slightly 

 branching with the apparent branches up to 2 cm. long and about 

 0,5 cm. thick, mostly however shorter and frequently thicker. But 

 the specimen thus, as a matter of fact, represents a crustformed, 

 not branching alga, which is developed round a branching one. 

 Even tubes of worms which have attached themselves to the host 

 plant are often encompassed individually. Sometimes some branch 

 or other of the host plant sticks out of the encompassing crust, 

 but also such ones are soon completely covered by Ph. investiens. 

 In host plants more densely branching, e. g. in L. Ungeri, the 

 whole of the alga is encompassed in a lot, or some projecting 

 branch or other individually. Younger specimens, e. g. of L. gla- 

 ciate, which have attached themselves to a stone are sometimes 

 almost wholly encompassed together with the stone. Also speci- 

 mens of some of the said species which are attached to the bottom, 

 or lying closely associated on the bottom, are often collectively 

 covered as with a mantle by Ph. investiens. 



A host plant thus encompassed is gradually attacked by ani- 

 mals, particularly boring mussels, by which it finally disappears. 

 We have then only to deal with the encompassing alga, which 

 now consequently represents a Ph. investiens apparently freely 

 developed, more or less hollow or with an opening generally in 

 the part turning downwards. As a general rule, however, this is 

 only the case when Ph. investiens encompasses in a lot the whole 

 bulk of a densely branching host plant, whereas in a sparsely 

 branching one the outer branches encompassed for the most part 

 remain undissolved. As a matter of fact, these branches are so 

 closely encompassed by Ph. investiens that in a fracture the surface 

 of the latter often conveys the impression of an almost parenchymatic 

 mass or of a new thickening layer of the host plant. 



Also Ph. investiens is attacked by the same animals that 

 have caused the decay of the host plant, so that the original crust 

 of the alga in question will frequently only form a tissue perforated . 

 by animals in every direction. But upon this crust are at the 



