32 RHODOMELACEiE. v. 



from it. These wheel-like slices, floated in a drop of water, may then be placed 

 under the compound microscope and examined. In slicing dried specimens, it is 

 best to cut the stem, if possible, before it be moistened ; as a thinner and cleaner cut 

 can then be made, and the risk avoided of the too rapid decomposition from the 

 fresh water. When the cells refuse to resume their proper shape on remoistening, 

 a drop of muriatic acid will frequently, but not always, expand them. 



Nearly 300 species of Polysiphonia are to be found described in various books, — 

 Kutzing has collated 248 in his latest work. Of these, perhaps one-third are false 

 species, founded either on solitary or on insuflicient specimens. The whole require a 

 careful revision and examination of the original materials. As in all large genera, 

 it will be found that some species are very constant to certain characters, while 

 others are so variable that it is nearly impossible to limit them within a short spe- 

 cific phrase. Of this last character are many Polysiphonice^ and the knot of diffi- 

 culty has too often been cut by splitting such species into several, a practice which, 

 once admitted, leads to continual dismemberment. I shall endeavour to avoid 

 unnecessary division in defining the American species. 



Subgenus 1. Oligosiphonia. Primary tubes, four only. (Sp. 1 — 17.) 

 * Stem visihly articulate throughout, with pellucid dissepiments. (Sp. 1 — 13.) 



1. PoLYSiPHONiA urceolata, Grev. ; filaments rigid, setaceous, full-red, much 

 branched, loosely bundled ; branches subdichotomous, furnished with short, alter- 

 nate, patent or recurved decompound ramuli ; internodes four -tubed, those of the 

 branches 3-5 times longer than broad, of the ramuli very short ; conceptacles 

 stalked, urn-shaped, with a projecting narrow orifice ; tetraspores in the ultimate 

 ramuli. Grev. Fl. Edin. p. 309. Harv. Phyc. Brit. t. 167. Kiitz. Sp. Alg. p. 824. 

 /3. jyatens ; with the lateral ramuli more numerous, strongly recui'ved, or revolute. 

 P. patens., Grev. Kiitz. I. c. Conferva patens, Dillw. t. G. 



Hab. Arctic Sea Coast, Dr. Sutherland! Prince Edward's Island, Dr. Jeans! 

 Halifax, W. H. H. Longbranch, New Jersey, Miss Morris. yS. at Monterey, Cali- 

 fornia, Dr. Coulter! (v. v.) 



Tufts large, bushy and dense. Fronds from 6 to 8 inches long, or more, twice 

 the diameter of human hair, decompoundly branched, generally without a leading 

 stem ; the branches alternate or subdichotomous ; lesser branches subdistant, alter- 

 nate or unilateral, multifid. Internodes in the middle part of the filament 4-6 times 

 as long as broad, in the branches 2-3 times, in the ramuli very short. Tubes 4, 

 broad, with very narrow interspaces. Conceptacles urnshaped, with a prominent, 

 contracted orifice, shortly stalked, scattered over the lesser branches and ramuli. 

 Tetraspores wider than the places where they occur, immersed in the ramuli in a 

 single row. Colour Avhen growing a clear blood-red, becoming dark reddish brown 

 or even black in the herbarium. Substance rather rigid, not lubricous. It does 

 not adhere strongly to paper in drying. 



