THE AERIAL ALGÆ OF ICELAND 435 



points out (1914, p. 297 1 that P. crispa is a saprophytic species tliat 

 only attains its full development where thcre is plcnty of organic matter. 

 Helgi Jonsson, too, mentions (1898, j). 360) that the species is very 

 widespread in Iceland in piaces abounding in manure. 



I have found very large tlialli of this species, thus in sample 121 

 (earth, SeycMsfjorciur i where one specinien had a diameter of 5 cm when 

 fulh' extended. 



Prasiola furfuracea FI. dan.) Men. Imhauser 1889, p. 266, 287 

 Heering in Pascher, Siisswasserflora Heft. 6, p. 57. 



E. Icel. 113 — S. Icel. 353 - Vestmannaeyjar 406. 



This species dilfers from the preceding one by its thalli which as 

 a rule are much smaller and attached tO the substratum b\^ a more 

 or less distinct stalk-like part, while the Hormidium forms are very 

 slightly developed. Thus t3'pically devcloped it occurred on stones in 

 fences round a couple of farms, and on rocks below bird-clift's on the 

 Vestmannaeyjar. 



PujMTialy maintains (1924, p. 230) that P. leprosa Kiitz. is a species 

 quite distinct from P. furfuracea, while most modern authors following 

 Imhauser regard the two species as identical. He refers certain pleuro- 

 coccoid forms from chalk clitTs to Prasiola leprosa, amongst others 

 Pleurococcus calcarius Boye P. (1915, p. 320). It is probably right that 

 this species must be regarded as a stage of a Prasiola, a possibility 

 which I already referred to in 1915. But I cannot see that Puymaly 

 has pointed out characters by which pleurococcoid stages of the diff'erent 

 Prasiola species may be distinguished from each other, and when these 

 stages alone occur in a growth without further developmental stages, 

 I think it is impossible at the present juncture to say what species you 

 have before you. 



Such a pleurococcoid form I have found on stones near the shore 

 on Ihc Vestmannaej'jar (sample 405). 



H.Jonsson states (1903, p. 354) that he has found P. furfuracea in 

 several piaces along the shores of Iceland on rocks, often in company 

 witli P. stipitata. 



Chætophoraceæ. 



Pseudendoclonium submarinum Wille. Wille 1901, p. 29, Taf. III, 

 fig. 101-134. Wille 1910, p. 282. 



Vestmannaeyjar 404, 405. 



The species was originally described by Wille from Drobak in 

 Norway where it formed coatings on breakwater stakes and other wood- 

 work in and near salt water, which macroscopically greatly resembled 

 Pleurococcus layers. Later on WMlIe found the species near Trondhjem 

 in Norway (1906, p. 17) and in France (1910. p. 282). It has besides 

 been observed by Helgi Jonsson (1903, p. 358), in Iceland, E. Icel. 

 Djupivogur) and by F. Collins in North America. In all these localities 

 it grew on woodwork, Wille, however, found it on the brick walls of 

 an aquarium in F'rance. 



