485 



traire incolore,« and the same may be said of the Færoese material 

 and of Prasiola crispa f. terrestris. 



Tbough Wil le (I. c. p. 1.'}) writes witli reference lo his formå 

 submarina: — ■ »Es kann vielleichl Zweifel daruber herrschen, warum 

 sie nicht als selbståndige Art aufgefuhrt werden soli, da sie keinerlei 

 Obefgang aufweist zu Prasiola crispa (typische Flåchenform), welche 

 aucb keineswegs mil ihr zusammen vorkommt,« il is quite natural, 

 al any rate now thai the typical plate-form has also been found, lo 

 refer it lo Prasiola crispa, with which it is very closely allied. The 

 fresh-water material from damp roofs in Thorshavn bears consider- 

 ahle rcsemhlanee to the marine form; as lo the differences which 

 exist belween them I mav point out the following: — In the Hormi- 

 <//////! -filaments the eells are altogether somewhat longer, being gene- 

 rally about ] /-2— 3 /4 times as long as broad, but cell- filaments also 

 occur in which the eells are as short as those in the salt-water 

 specimens. Rhizoids are comparatively rare in the fresh-water 

 material, tbough they may sometimes be met with, as I have shown 

 on Plate IX, fig. 2, a, and Gay (1. c. figs. 126 — 127) also figures some 

 which correspond exactly with those in the marine form. The 

 reason why the latter form is so amply supplied with rhizoids may 

 possihly he explained by the faet that the alga growing, as it very 

 often does, in much exposed situations, must altach itself firmly 

 to the rock so as to be able to withstand the force of the waves. 

 The plate-form (Prasiola- stage) of the marine specimens exactly 

 resemhles that of the land- form in the arrangement of the eells, 

 but it hardly attains to so large a size as in the latter. Lastly, I 

 may liere point out that the Gayella- stage has not hitberto been 

 found in the land -form. I am thercfore of opinion that on the 

 strength of these differences the forms referred to Prasiola crispa 

 ought to he divided into two sub- species, the marine suhspec. 

 marina, and the land -form, which may be cailed suhspec. terrestris. 



Further, the plant which Batters (1. c. p. .'58, tab. VII, fig. 8) 

 calls Ulothrix discifera, judging from the specimens which he sent 

 to Rosen vinge asking if they could possihly be Gayella, must 

 belong to the present species; there are no rhizoids in bis figure, 

 tbough the examples of his plant which are liere in Copenhagen are 

 richly provided with them. Schizogonium radicans Foslie (1. c.) 

 likewise belongs to the present species. Foslie' s specimens, of 

 which there are two in the museum in Copenhagen, are precisely 

 similar to mine. Ulothrix discifera Kjellm (I. c), on the other band, 



31* 



