THE FRESH-WATER CYANOFHYCEÆ OF ICI.I.AXI) 309 



due to a misundcrstanding in that none of the Icelandic hot springs 

 deposits lime, but exclusively silicious sinter (TKoroddsen 1910 p. 117). 



I can still mention two more synonyms, viz.: Sphærozijga Japeti 

 Liebm. and S])hæro:!jga thcrmamm Liebm. Both species are figured in 

 Flora danica, tab. 2399, and were referred to by Liebman (1840 p. 338 j. 

 In the herbarium Johs. Sclimidt already directed attention to the faet 

 that these two species were identical with Hapalosiphon laniinosus, and 

 I have had opportunity of examining some samples, collected by Steen- 

 strup on the localities mentioned by Liebman, and upon which was 

 written Sphærozijga n. sp. in Liebman's band. I take it for granted that 

 these are the original specimens of the two species established by Lieb- 

 man and can thus verify Schmidt's note regarding the actual position 

 of these s])ecies in the system. 



As already alluded to, the species in question can be found under 

 three essentially dilfcrent forms: 



L f. typica, the typical Hapalosiphon form with branchings, distinct 

 difference between the primary and secondary threads, the latter 

 being thinner and more cylindrical than the former the cells of 

 which are inflated and more or less spherical. Heterocysts well 

 developed. Sheaths, as a rule, firm, distinct, and colour a pronoun- 

 ced violet with chlor-zinc-iodine (fig. 15, a). 



2. f. anabænoides, the Anabæna-like form (= Aiilosira thermalis West) 

 without any branching. All the threads almost similar, with more 

 or less spherical cells and distinct heterocysts. The cells are largest in 

 the middle of the trichome, decreasing as a rule towards the apices. 

 In this as well as in the last form spirally coiled threads are not 

 infrequently met with as alreadv described and figured by Schwabe 

 (1837 p. 126, tab. II, fig. 14 a). 



The vaginæ are as a rule more or less confluent and colour 

 faintly or not at all with chlor-zinc-iodine (fig. 15 b). 



3. f. phormidioides, the phormidium-like form in which all the threads 

 are almost similar, without heterocysts, with constrictions between 

 the cells which often are feebly constricted in the middle. The 

 sheaths confluent, do not colour with chlor-zinc-iodine (fig. 15 c). 



Between these forms numerous transitions exist, and I therefore 

 presunie, like Bornet et Flahault, that they all belong to the same species. 

 The proof of this can hardly be adduced in any other way than by 

 means of pure cultures, but as far as I know nobody has as yet at- 

 tempted this with regard to Hapalosiphon laniinosus. 



This species is a cosmopolite among the thermal algæ fElenkin 1914). 

 It has been found on all continents, but up till now in no arctic or 

 antarctic region, e. g., neither at the hot springs in Greenland nor Spits- 

 bergen. From two piaces only is it recorded as an occurrence of non- 

 thcrmal water, viz., the Hhine (Lauterborn) and a stream on Celebes 

 (Weber-van Bosse 1913). 



Lowenstein (1903 p. 317^ experimented on and closely investigated 

 the limits of temperature within which this alga might thrive. He found 

 that 52*^ C. was its maximum, whereas it is capable of withstanding 



