1886-87.] Mr E. M. Holmes on Sphacelaria radicans. 79 



Bemarks on Sphacelaria radicans, Harv., and Sphacelaria 

 olivacea, J. Ag. By E. M. Holmes, F.L.S. 



The plant alluded to by Mr G. AV. Traill, in the above 

 paper, under the name of Spliacclaria olivacea, J. Ag., does not 

 appear to have been well understood by any of the preceding 

 algologists who have described it, except Dillwyn. 



Agardh, in his Species, Genera, et Orclines Algarum, p. 31, 

 mentions S. olivacea, and a variety radicans, distinguished by 

 its rather firmer filaments rooting from the upper portion, 

 but does not remark that it has a different habit of growth. 

 This rooting character, however, is figured by Kiitzing, under 

 S. olivacea ! 



In English Botany, two figures are given, one of which, 

 tab. 2430, represents >S^. olivacea, as having a more flaccid 

 character than *S'. radicans, tab. 2429. In the description of 

 the species there given, the author remarks that >S^. olivacea 

 approaches so nearly to 8. radicans, that the creeping habit 

 of the latter seems to constitute the only real difference. 

 8. radicans is described as growing on sand-covered rocks, and 

 8. olivacea on rocks and larger algse. 



It would thus seem that both the plants of English Botany 

 grow under water, one being rather more rigid than the 

 other. 



Harvey, in the Phycologia Britannica, combines these two 

 under the name of Sphacelaria radicans. He remarks that 

 8. olivacea of British authors is less disposed to throw out 

 radicles than the other, but that the >S'. olivacea of Lyngbye 

 may be a different plant. I cannot find, however, that 

 Lyngbye describes a species under this name. He doubt- 

 fully identifies his >?. cmspiitula with Dillwyn's aS'. olivacea 

 {Dillw. Int., p. 57, suppl. tab. c). 



More recent authors* follow Harvey in uniting the above 

 two forms under the name of 8. radicans. The difference 

 in habit of the 8. olivacea of Dillwyn from that of 8. radicans, 

 Harv., is very marked. As I have seen 8. olivacea, Dillwyn, 

 growino; in caves at Berwick, it forms a dense coat on the 

 walls of the cave like velvet plush, of a fine brown colour, 



* Farlow, Marine Algcc of New England, p. 76 ; Hauck, Meercsalgen der 

 DeutsMand, p. 343. 



