THE AERIAL ALGÆ OF ICKLAND 433 



Stichococcus bacillaris Niig. Någeli 1849, p. 76, Tab. IV, G. 

 N. Icel. 243 — W. Icel. 349 — S. Icel. 287, 395. 



In Denmark this species grows on various substrata, but especially 

 on the bark ol" living trees and on wood, and by preference in piaces 

 with very subdued light, e. g. in dense woods. In Iceland it is of much 

 rarer occurrence which is perhaps due to the faet that suitable habitats 

 are not comnion here. In the birch woods the light mav possibly be 

 too strong for it, and all woodwork is as a rule exposed to the light and 

 wind in Iceland. I have only found it in four localities, viz. 1) in a cave 

 formed by the action of the waves bj' the shore near Hiisavik (243), 

 2) on a fence pole at MoiVuvellir in Kjos, and 3) on a telegraph pole 

 at Borgarnes, in both the latter cases quite near the ground, and finally 

 4) on the lower part of the wall of the old factory near Reykjafos. 



Prasiolaceæ. 



Prasiola Ag. 



The taxonomy of the genus Prasiola has long been a matter of 

 controversy and the discussion is hardly closed yet. The tendency has 

 in the main been towards assembling the numerous forms described 

 according to two lines. In the first place it has been recognised that 

 each species couid occur in a filamenlous form (Hurmidium), a band- 

 shaped form (SchizogoninmJ, and a Hat expanded form (Prasiola). To 

 these may be added a Pleurococcus-like form, often confused with Pleiiro- 

 cocciis viilgaris Men., thus by Chodat (1909\ and by Brand (1925). 

 In this way the number of genera has been reduced to one, viz. Prasiola. 

 In the second place various authors have realised that several of the 

 species established cannot, in faet, be dislinguished from each other, 

 and so nowadays abt. 4—5 aérial species are taken into account. Even 

 the justification of cerfain of these species is sometimes questioned, just 

 as also the various authors do not quite agree as to what characters 

 should be employed to distinguish them. 1 shall not here enter more 

 fully into the extensive literature, but refer the reader to the thorough 

 researches of Imha user (1889) and Brand (1914), who cite the litera- 

 ture then available. 



Prasiola crispa (Lightf.) Men. Brand 1914, p. 308. 

 Schizogoniuni crispum Gay 1891, p. 86. 



— murale — — - 87. 



— radicans Chodat 1909. 



E. Icel. 14, 15, 40, 77, 78, 92, 112. 114, 121, 131 — N. Icel. 135, 

 161, 162, 172, 173, 185, 196, 197. 216, 217, 242, 252- N.W.Icel. 261, 

 268 — W. Icel. 297, 298, 307, 309a, 325 — S. Icel. 275, 282, 283, 287, 

 295, 352, 372, 381 — Vestmannaeyjar 408, 409. 



Above 1 have only given a few of the numerous s^^nonyms of this 

 species; the reader will be able to lind the rest from the citations given. 

 After it had been established by Imhåuser's investigations that the 

 Hormidinm forms were merelj'^ imperfectly developed Prasiolæ, Gay thought 

 nevertheless (1. c), that two aerial forms could be dislinguished, which 



