— 198 — 



Hypoglossum tenuifolium (Harv.) J. Ag, 



J. Agardh, "Spec. Alg.'\ vol. 3, pars 3, 1898, p. 186. 



Delesseria tenuifolia Harv., "Nereis Bor.-Am.", II, p. 97, t. XXII. 



This fine, delicate species was found rather abundantly in deep 

 water in the Sound between St. Thomas and St. Jan. When living 

 it had a bright yellow-greenish colour, but on drying it took on a 

 reddish tinge. 



The thallus consisted of a single layer of cells only, with the 

 exception of the midrib which consisted of three layers (Fig. 15 C). 

 Plants with tetraspores, antheridia and cystocarps were found. 



Fig. 15. Hypoglossum tenuifolium (Harv.) J. Ag. 



A, part of an antheridial plant (120 : 1). B, transverse section of an antheridial stand 

 (270 : 1). C, transverse section of the midrib in the leaf (120 : 1). 



Of tetrasporic plants I have only had dried material at my 

 disposal. The tetrasporangia occurred close to the midrib, symme- 

 trically arranged on both sides of it. They begin to be developed 

 in about the middle of the leaf and continue their development 

 towards the apex of the leaf, becoming here younger and younger. 



The male plants had the antheridia on both sides of the 

 midrib; they occurred as low dense cushions covering the surfaces 

 of the cells on both sides. They are arranged rather regularly and 

 most often following every second segment in the leaf (Fig. 15 A), 



