THE FRESH-WATER CYANOPHYCEÆ OP ICELAND 313 



Stigonema informe Kiitz. 



Hornet et Flahault, Revision III p. 75. 



Sirosiphoii lacustris Rab. Alg. nr. 611. 



N. Icel. Skutustaåir, small pond, temp. 19^ '^/7 1914. 

 Area: Eur., As., Am., Austr., Lappland, Færoes, Greenland. 



The specimen found had the following dimensions: main threads 

 c. 75 fi in diam., lateral branches c. 45 //, cells 10 — 15 //, hormogones 

 c. 13 fi in diam. and varying length, frequently very long which may 

 be due, however, lo the faet that \ve have to do with chains of hormo- 

 gones. These dimensions are, on the whole, in accordance with the 

 diagnosis in Bornet et Flahault (1. c.) The hormogones only are some- 

 what thinner than those recorded by the afore-mentioned authors. Stock- 

 mayer (,1909 p. 66), who has had abundant material of this species at 

 his disposal, states that he has often found hormogones 8—12 fi in diam., 

 15 //, on the other hånd, but a few times. He opines that St. mamil- 

 losuni may perhaps be but a varietj' of this species. 



S. informe has generally been found on moist rocks, but also in 

 water or on trunks of trees. The Icelandic specimen originales from 

 waler, and this may probably account for its sheaths not bcing so brown 

 as in Rab. Alg. nr. 611. 



Stigonema mamillosum (Lyngb.) Ag. 

 Bornet et Flahault, Revision III p. 77. 



E. Icel. Sey6isfj6r3ur, bog at 300 m. above sea-level, on moss 

 ^^/e 1914. — Fljotsdalur, on rocky wall over which water was trickling 

 3% 1914. RauSara, in puddles of water on stones ^^/i 1897 (H. J.)! 



Area: Eur., As., Am., Færoes, Lappland. 



In all 3 samples the species was but scantily represented, but it 

 was abundantly provided with hormogones, 11 — 13 i( in diam. and up 

 to 84 // in length. I have compared the sam])les with an original spe- 

 cimen in Herb. Lyngbj'e, exhibiting short hormogones, but otherwise 

 bearing a close resemblance to the Icelandic specimens, as well as with 

 a sample determined by Flahault. 



On the original specimen in Herb. Lyngb. numerous hormogones 

 occurred, being all about 13 /< in diam. and 45 /< in length. Bornet et 

 Flahault particularly emphasize the length of the hormogones, being of 

 the opinion that this dimension is very constant. Stockmayer (1909 

 p. 66) pronounced against this view in that he actually found a conside- 

 rable variation in the length of the hormogones in S. informe. (The 

 exact relationship between S. informe and S. mamillosum may be left 

 an open qucstion until more detailed invcstigations can be undertaken.) 

 Personally I am inclined to believe that the diameter of the hormogones 

 should be a much more constant character than their length, as seriated, 

 more or less confluent hormogones are a common occurrence in e. g. 

 S. informe. But even the diameter of the hormogones may, of course, 

 be somewhat variable. I have therefore no hesitation in referring the 

 specimens found to the species in question. 



On the slrength of their knowledge regarding the distribution of 

 S. mamillosum, Bornet and Flahault slate that it appears to be confined 



The Botany of Icelnnd. Vol. II. 21 



