THE AÉRIAL ALGÆ OF ICELAND 423 



Tribonema bombycinum (Ag.) Derb. et Sol. Heering 1906, p. 131. 

 E. Icel. 55 c, 84, 86, 88, 91, 100. 



The species was cxtremely common on dripping rociis. Sample 55c 

 was collected in a small rocky cave with constantly trici<ling water. Il 

 was only found al Ihe moulh of Ihe cave. not in tlie inlcrior where 

 the light was fainler. All the samples menlioned al)ove originale from 

 E. Iceland, bul there is no doubt thai the species is just as common on 

 irrorated rocks in other paris of the Island, but il was only in E. Ice- 

 land that I had the opportunily of examining Ihis kind of localily. In all 

 the samples it occurred as formå gemiina Wille with a lilamenl thickness 

 of 6-8/*. 



As regards Ihe common occurrence of the species as an aérial alga 

 I refer the reader lo Puymaly 1924 p. 177. I shall merely add that 

 frequently it occurs in cultures of soil-samples in nulrienl media con- 

 taining mineral substances, as carried out by Hrislol (1920). I myself 

 have found il in similar cultures of soil from Iceland. Il furlher appears 

 from Miss Bristols investigalions lliat it will survive strong desiccation. 

 viz. up to 24 weeks. It is probably ils aplanospores or zygospores tlial 

 have this great power of resistance to desiccation. In Ihe soil in Xalure 

 the spores will no doubt be able to survive very long and will easily 

 develop into »formations passagéres«. (Comere 1913, p. 10). I found il 

 in Denmark in such a localily. (1915, p. 313). 



Tribonema tenerrimum (^Gay) Heering. Heering 1906, p. 130. 

 E. Icel. 91. 



The threads found of this species had a thickness of 4—5 //, and 

 the cells were 4—5 times as long as broad. It occurred in company 

 with T. bombgciiuim on a rocky wall with water Irickling down il. 



Isokontæ. 



Protococcales. 

 Protococcaceæ. 



Coccomyxa Schmidle. 



The genera Gloeocijslis Niigeli (1849) and Coccomyxa Schmidle 1901) 

 are, in the opinion of most aulhors, closely related. and in recent limes 

 several aulhors have uniled Ihem, Wille under Ghto/??//.!-« 1 1909. p. 38), 

 and Puymaly under GloeocyslLs (1924. p. 212 ff.). In the diagnosis ol Ihe 

 genus Gloeocijslis the following are the chief features »Zellen kugelig 

 ... in ... . Familien vereinigl, die von einer Blase umschlossen und im 

 Innern in der Regel aus wiederholl in einandef geschachteltcn Blasen 

 gebildet sind«. 



As characters perlaining lo the genus Coccomijxa in conlrast lo 

 Gloeocyslis Schmidle gives 1) the lack of a pyrenoid in Ihe chromalo- 

 phore and 2) a dillerent mode of division. The first-namod ditlerence 

 will in many cases be diflicult to demonslrale wilh cerlainly. liuis I 

 ara not convinced that it will be possible in the long run lo keep Coc- 



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