— 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 plurilocular 

 sporangia in June. 



In his List of the marine Algæ of Berwick-on-Tweed *) 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 curta Fosl.) is identic with Isthmoplea 

 sphærophora with plurilocular sporangia, and points out the great resem- 

 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. 1 

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

 sphærophora, as they precisely 

 agree with the plants bearing 

 unilocular sporangia in every- 

 thing except that they have 

 plurilocular 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- 

 phores are the same. Conse- 

 quently Fosliea curta must be 

 regarded as identical with Isth- 

 moplea sphærophora. Reinke 



Fig. 18. Isthmoplea spærophora (Harv.) Kjellm. 

 Transverse section of the frond showing the 

 development of the pluricular sporangia. 

 Compare the text. (316:1.) 



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

 moplea sphærophora, the 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. sphærosphora. 1 

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

 whether they bear unilocular or plurilocular sporangia, is usually narrower 

 below. The axis of plants with unilocular sporangia measured below 

 30 p and about the middle of the frond 40 — 45 jut, and specimens with 

 plurilocular sporangia had an axis below 25 p. 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. 



J ) Berwickshire Naturalists 1 Club Transactions 18S9. 



