1920] Setchell-Crardner : Chlorophyceae 181 



pyrenoids; multiplication by fragmentation and by akinetes; repro- 

 duction by 2-ciliated zoospores with stigmata; gametes unknown. 



Kuetzing, Phyc. Gen., 1843, p. 261, Ueber syst. Eintheil. der Algen, 

 1843a, p. 75 (nomen nudum). 



The genus Rhizoclo7iium, as founded by Kuetzing but without 

 special indication of type species, is one of the simplest of the Clado- 

 phoraceae. It consists ordinarily of species with simple, unb ranched 

 filaments whose segments are provided with comparatively few nuclei. 

 The rhizoidal branches may, or may not, be readily found. In the 

 absence of these it is sometimes difficult to be certain of the genus. 

 The species may usually be distinguished from Chaetomorpha by their 

 characteristically cylindrical, never swollen, segments with a smaller 

 niunber of nuclei in each, as well as by their different texture and 

 tendency to a horizontal habit. The branched species resemble Clado- 

 phora, but the branches push aside the main axis and continue the 

 direction of the main filament. The species of Rhizoclonium inhabit 

 both the fresh and the salt waters. 



The separation of the species of Rhizoclonium one from another 

 presents certain difficulties which are increased by the fact that very 

 little seems to have been done in the culture of species of this genus. 

 The following characters have been considered : (1) color, (2) texture, 

 (3) straightness or crispate character of the filaments, (4) diameters 

 of the segments, (5) proportions of length to breadth of the segments, 

 (6) varying thickness of the walls of the segments, (7) varying num- 

 ber of nuclei in the segments, (8) presence or absence of long (true) 

 branches, and (9) presence or absence of rhizoids. Of these char- 

 acters, it seems from our present imperfect knowledge that 1, 2, 3, 8 

 and 9 are the more dependable characters, and that 4, within certain 

 limits, is very helpful. Characters of 5, 6, and 7 will vary within wide 

 limits in the same plants, according to whether they are actively divid- 

 ing or passing into a quiescent condition, as one of us (Gardner) has 

 experienced in growing Rhizoclonium luhricum in the laboratory, and 

 as Brand (1908, p. 66) has stated as the results of his cultures. 



The principal account of Rhizoclonium of more recent years is that 

 of Stockmayer (1890), but his arrangement of the marine species is 

 not satisfactory to most students. The general disposition of the 

 marine species made by Rosenvinge (1893, p. 911 et seq. and 1894, 

 p. 126-129) seems based on more certain characters and has been 

 generally followed. F. Brand (1908, p. 45 ct seq.) has made some 

 important studies through cultures, testing certain of the characters 



