THE AÉRIAL ALGÆ OF ICELAND 419 



Nitzschia vitrea Norman v. salinarum (inin. (.1. und (Irun. Arct. 

 Diat. p. 94. Van Heurck Syn. PI. 67, lig. 12. 



Veslmannaeyjar L. 401, L. 403, L. 410. 



According to the literature this species is a brackish water and 

 marine species. Østrup had previously l'oiind it in a sample from 

 fresh water from the Yestmannaeyjar. Since it was foiind in numerous 

 specimens with cell contents in the samples menlioncd, it has been 

 established with certainly that it can grow on land. Even Ihough il 

 was found at rathcr a great height abovc the level of the sea (20 mi it 

 is quite possible that it may be reached by the salt water spray in 

 stormy weather, and this may possibly be a life condilion for it. 



CHLOROPHYCEÆ. 



There is a strong tendency al present to try to revive old forgollen 

 names of species and genera within Ihe green algæ in order ti> iinprove 

 the nomenclature as has been successfully done to a great exlenl wiliiin 

 the phanerogams. Among the unicellular algæ, however, the matter is 

 much more difticult, partly because the descriptions and figures in the 

 earlier literature are most imperfect, and partly because original spe- 

 cimens are often lacking. And even if such are found in the form of 

 exsiccata, it is often very diflicult, even upon most careful c.\amination, 

 to arrive at decisive results by the aid of them, as has been correclly 

 pointed out e. g. by Brand (1924, ]). 324). In my opinion, therefore, 

 one cannot be crilical enough with regard to that kind of invesligalions. 

 and I shall have occasion to express niy doubts as regards several of 

 them under the individual species. 



The present investigalion has been based almost exclusively on 

 material collected in the dried condilion by myself during the summer 

 of 1914. While samples thus collected remain almost unchanged in the 

 case of true aérial algæ for weeks, months, nay often longer periods, 

 because the algæ still remain alive, it is quite otherwise after the lapse 

 of several j'ears. Then the cells will gradually die, the cell contents 

 shrink somewhat, and even after prolonged soaking in water it is diflicult 

 to recognise the exact structure of the cell contents. especially chroma- 

 tophores, pyrenoids and cell nuclei. Spccial melhods nuisl be resorled 

 to in order to soak the cells and attempt by chemical means to make 

 the desired structures appear. For soaking Lagerheims lactic acid 

 method (1888) has yielded excellent results especially with succeeding 

 rinsing and treatment with potassium tri-iodide. For the demonstration 

 of pyrenoids with starch (cf. Brand 1925' I have very successfully 

 employed chlor-zinc-iodine which e. g. in Prasiohi will bring out the 

 pyrenoid surrounded by blue grains of slarch very handsomcly. 



As was to be expected, the method indicaled by (ieitler in which 

 nitrate of silver was employed lo make the chromalttphores appear dis- 

 tinctly, proved unavailable in the case of dried material. 



