THK AKRIAL ALGÆ OF ICELAND 



429 



Tréboux advocates the conception that thc relationship between 

 the fungus and the alga in a lichen is one of simple parasitism, especi- 

 ally on the ground that the alga thrives far better in the open than as 

 a gonidium. However, this view does not seem to meet the case in 

 Iceland where lichens thrive well while free living algæ are practically 

 unknown, and we cannot entirely dismiss the idea that the algæ enjoj^ 

 no inconsiderable protection from the fungus against the difficult climatic 

 conditions. 



Trochiscia hirta (Reinsch) Hansg. Boye Petersen 1915, p. 325, Tab. II, 

 fig. 21-24. West 1904, p. 203, fig. 82 G. H. 



Acanthococcus hirtus Reinsch 1886. p. 240? 

 Pleurococcus vestitus Lagerheim 1882, p. 78? 



— — Wittr. et Nordst. Alg. exsicc. No. 446? 



N.Icel. 216 — N.W.Icel. 261 — S. Icel. 275,292 — Vestmannaeyjar 400. 



The present species has previously been mentioned by me (1. c.) and 

 on comparing the Icclandic material with my samples from Denmark I 

 have found the closest agreement. I have again compared my material 

 with Wittr. et Nordst. No. 446, but with the specimens in this sample 

 the agreement is not quite satisfactory, the spines on the surface of the 

 cells being considerabl}' coarser here than in the Icelandic and Danish 

 samples I have had under observation. In the small table below I give 

 the dimensions of the cells. 



Diameter of cells 



Number of spines in 10 jM 

 Length of spines 



Wittr. et 



Nordst. 



Nr. 446 



13— 15,4 /.t 



abt. 4 



abt. 2 /( 



Sample 292 



from 



Iceland 



Sample 216 



from 



Iceland 



15,4— 24,2 /t 



7—10 



O.s— 1,6/^ 



20 /f 



abt. 9 



abt. 0,(3 fi 



From 

 Denmark: 

 Dj'rehaven 



23/.< 



abt. 9 



abt. 1 ,11 



While I have found cells both in the Icelandic and thc Danish 

 material in which the numerous chromatophores could be plainly seen, 

 this was not the case with the exsiccatum. Hence I am not quite certain 

 of the identity of these forms though I cannot conclusively show that 

 they are not variations due to difference of life conditions. The main point 

 here is how far the form in Wittr. et Nordst. is furnished with one or 

 several chromatophores, and whether or not there are pyrenoids. Further 

 investigations may perhaps clear up this point. 



In Denmark I have found the species on woodwork, tree-trunks, 

 and thatched roofs. In Iceland I have also collecled it from woodwork 

 (261, 292;, but likewise on large stones, especially in piaces protected 

 against intense desiccation. (216, 275, 400). 



Oocy staceæ. 



Kepatococcus bicaudatus (A. Braun) Boye P. n. comb. 

 Dactvlococcus bicaudatus A.Br. in Rab.Fl.eur. alg. Sect. III, 1868, p. 47. 



