182 University of California Puhlications in Botany [Vol.8 



mentioned above as to their constancy or variability. After consider- 

 ing all the data possible it has seemed best to take a somewhat nar- 

 rower view of specific limits than has been prevalent and divide our 

 west coast plants among five seemingly distinct species. 



Key to the Species 



1. Filaments flaccid or lubricous, straight or flexuous, light or yellowish green 2 



1. Filaments rigid, contorted, dark green 5. R. tortuosum.. (p. 185) 



2. Layer fleecy, filaments flexuous, 10-35/i 3 



2. Layer lubricous, filaments straight, 25-50^ 4. R. lubricum (p. 185) 



3. Rhizoidal branches frequent, often 2-3 septate 1. R. riparium (p. 182) 



3. Rhizoidal branches scarce, when present non-septate 4 



4. Filaments 10-14^ 3. R. Kerneri (p. 185) 



4. Filaments 20-30At 2. R. implexum (p. 183) 



1. Rhizoclonium riparium (Roth) Harv. 



Filaments pale green, expanded on the substratum, flexuous, inter- 

 twined into a fleece ; segments 20-25/x diam., rarely slightly greater 

 or smaller, usually once or twice as long as broad; branches and 

 rhizoids frequent, often 2-3-septate. 



In skein-like masses on cliffs or hard clay banks, often among other 

 algae in the littoral belt. Alaska to central California. 



Harvey, Phyc. Brit., vol. 2, 1849, pi. 238 (binomial attributed to 

 Kuetzing) ; Collins, Green Alg. N. A., 1909, p. 327 (in part). Con- 

 ferna riparia Roth, Cat. Bot., vol. 3, 1806, p. 216 ; Dillwyn, Brit. Conf ., 

 1809, p. 69, pi. E. Rhizoclonium riparium var. polyrhiziim Rosen- 

 vinge, Groenl. Havalg., 1893, p. 913, f . 32 ; Collins, Green Alg. N. A., 

 1909, p. 328; Collins, Holden and Setchell, Phyc. Bor.-Amer. (Exsicc), 

 no. 2238. 



There is no question in our minds that the situation as to species 

 of Rhizoclonium on the Pacific Coast of North America is very similar 

 to, if not perhaps identical with that on the Atlantic Coast of the same 

 continent and on the Atlantic shores of Europe. There are at least 

 two sets, or groups, of plants differing somewhat in dimension and 

 in habit. One of these sets of forms is usually referred to Rhizoclonium 

 riparium and the other to R. tortuosum. This would be reasonablj^ 

 satisfactory, if no previous conceptions existed to be considered. The 

 ■ two species, however, as far as names are concerned, date back to the 

 early portion of the nineteenth century, viz., to the publications of 

 Roth (1806) and Dillwj^n (1809) respectively. Unfortunately no 

 type specimens are available to us and we can simply follow the 



