— 163 - 



on Ptilota and Laminaria digitata down to a depth of 10 fathoms. It has 



been gathered with unilocular sporangia in May —June and with pkuilocular 



sporangia in June. 



In his List of the marine Algae of Berwick-on-Tvveed ^) p. 58 Batters 



mentions the plurilocular sporangia of this species, saying: ,In the present 



genus the plurilocular sporangia are formed in the continuity of the 



branches", but he gives no further particulars. Reinke supposes (i.e.) 



that Fosliea curta (Pylaiella curia Fosl.) is identic with Isthmoplea 



sphrerophora with plurilocular sporangia, and points out the great reseni- 



blence of these two species. I have in SW. Iceland and S. Iceland met 



with specimens having plurilocular sporangia. These plants are fully 



agreeing with Fosliea curta (Fosl.) Rke. according to Foslie's description, 



figures (1. c.) and original specimens here at the Botanical Museum. I 



have no doubt at all that the specimens in question belong to Isthmoplea 



spluierophora, as they precisely 



a 



agree with the plants bearing 

 unilocular sporangia in every- 

 thing except that they have 

 |)lurilocular sporangia. The 

 size of the plants is the same, 

 the thickness of the filaments is 

 nearly the same, the ramifica- 

 tion, the structure of the frond 

 and the shape of chromato- 

 pho!-es are the same. Gonse- 

 ((uently Fosliea curia must be 

 regarded as identical with Isth- 

 moplea spha^rophora. Reinke 

 (1. c.) however points out some differences between Fosliea carta and Isth- 

 moplea sphasrophora. tlie main axis of the former being narrower below, of 

 the latter thicker below, and further he mentions that the branches of F. curta 

 are ending in a hairlike point (Haarspitze), wanting in I. sphaerosphora. 1 

 do not find any such difference. The axis of the polysiphonous specimens, 

 whether they bear unilocular or plurilocular sporangia, is usually narrowei- 

 below. The axis of plants with unilocular sporangia measured below 

 30^/. and about the middle of the frond 40 — 45/^, and specimens with 

 plurilocular sporangia had an axis Itelow :25 jl thick and about the 

 middle of the frond 40 — 60 fi thick. Both the plants bearing unilocular 

 and those bearing plurilocular sporangia have the branches in the same 

 manner tapering towards the apex, but never ending in a hair. 



Fig. 18. Isthmoylea spcerophora (Harv.) Kjelliii. 



Transverse section of tlie frond sliowing tlie 



development of the pluricular sporangia. 



Compare the text. (310:1.) 



') Berwickshire Naturalists' CJiib Transactions 1SS9. 



