296 JOHS. BOYK PKTKMSKN 



samples I have olien mct willi .l/nf/xr/jd-threads; hul I have not siir- 

 ceeded iii (letcniiininij; tluMii. 



Anabæna variabilis Kiit/. 



Hornet el Klaluuill, iU'vision IV p 22f). 



A. <)Scill(trioi(U's Wiltr. et Nortlsl. Alg. exsice. nr. l'.Hi. 



S. locl. Heykholt ' V7 185)7 H. J. ! Thinj^vallavatn. erratic in plank- 

 ton (Ostenf. et \Vesenb.-L. 1906 p. 1107). Menlioned by K. iielloc 1894. 

 Area: All continents. Greenland, Færoes. 



As lo tlu' linbitnl of Ibis species the Icelandic occurrences do not 

 olier mufli information. In Ibe literature it is statcd to have been found 

 under hii(hly varying eonditions, in pure fresh water as well as in 

 brackish water, moreover in hot s|)rings lemp. 32 *^— 42 " C. Bolilin 

 1901 p. 75) and llnally in earth from various regions of the world at 

 a (lei)th of unlil 30 cm. lEsmarcb 1914 p. 270, Bristol 1920 p. 62). 



Anabæna flos-aquæ Lyngb.; Bréb. 



Bornct et Klahault, Revision IV p. 228. Lemmermann, Kry])togamen- 

 flora d. Mark Brandenburg III p. 185. 



N. Icel. Myvatn, plankton; "water-bloom" ^^/t 1914, temp. 17". ^V? 

 1914 lem]). 16°. (irimshuMr at Myvatn, pond, plankton ^"/t 1914. lemp. 

 18". Slulnes in Myvatn, pond, |)Ianklon ''^7 1914. Geiteyjarstrond at 

 Myvatn, pond, plankton '^^t 1914, temp. 18". 



Area: Eur., As., Afr., Am., Greenland, Antarctic. 



A. flos-iujiuv and .1. Lemmermanni Hicht. are very closely relaled, 

 in faet so closely relaled thai I doubt whether they actually can be dis- 

 linguisbed from each olher. The form, which occurrcd in Myvatn and 

 in several of liie smaller ponds in ils vicinily, was in the main .1. //o.s- 

 aqiiæ, although it is impossible for me to sav whether A. Lemmer- 

 manni mav also bave been present. As Ihc main dilTerence belween the 

 two species Lemmermann (1910 p. 177) menlions the occurrence of llie 

 spores in series or in ones at the side of the heterocysts. On the pre- 

 sent material, however, this feature is difficult to observe as the mass 

 of spores is very dense. Should an atlcmpt be made to separate the 

 trichomcs by a pressure on the cover glass, they go as a rule (juite to 

 pieces, and we do not succeed in Ibis manner cither to see the arran- 

 gement of the spores in the trichomcs. However, in a number of cases 

 I have seen the spores dislinctly in ones al the side of Ihc heterocysts, 

 and I Iherel'ore refer the species in (jucstion to .1. flos-iuiiuv. 



Wlicn Ostenfeld and Wesenbcrg-Lund in 1903—04 had plankl(m 

 collected every fortnighl in Myvatn, this species was not found in the 

 lake which on the whole proved lo bo destitute of phyto-plankton 

 (Ostenf. and W.-L. 1906 p. 1143). When I visilcd the lake in 1914. il 

 s|)rang, on the other band, a grcat surprise upon me in the form of a 

 ralher exlensive 'Svater-bloom " formalion of Aiuilnrnti /los-aijUd'. In the 

 plankton samples this species prevailed almost exclusively, excepting a 

 small number of Rotiferæ .Xnuræai. 



There are now two conceivable ways of explaining this strange 

 discrepancy. Wesenberg-Lund opines thai all living beings in the lake 



