THE GREEN ALGAE OF NORTH AMERICA 385 



in a cell; oospores usually in two longitudinal series, 11-26 /j. 

 diam., including membrane. Fresh water. Fig. 141. Minn., 

 Cal. Europe. 



A plant of shallow, easily dried pools ; the oospores retaining 

 vitality for years, and germinating when again moistened. Of 

 wide distribution in isolated stations. Klebahn, 1899, divides 

 .S. annulina into two species, 6". crassi septa (Heinrich) Klebahn, 

 and 6". Braunii Kiitzing ; the former with filaments 27-35 V- 

 diam., 500-1200 p. long, oospores 11-19 /a diam., including mem- 

 brane, mostly 14 //., dissepiments thick, often with conical pro- 

 jections ; the latter with cells 42-65X250-1400 /x, oospores 13-26 

 p., mostly 17-19 /A, dissepiments relatively thin and even. 

 Whether there are two distinct species, or only two forms or 

 varieties of 5". annulina, is hardly certain ; in the former case it 

 would not seem that the name of ,S\ annulina should be given 

 up in favor of S. crassisepta ; all American specimens examined 

 are of the crassisepta type. 



Order VI. SIPHONALES. 



Fronds filiform, usually much branched or developing into 

 various forms, continuous without dissepiments in the vegeta- 

 tive condition, multinucleate, with many lens- or disk-shaped 

 chromatophores. 



KEY TO THE FAMILIES OF SIPHONALES. 



i. Sexual reproduction by motile gametes or unknown. 2. 



i. Sexual reproduction by non-motile oospores and motile sperrnato- 



zoids. 6. VAUCHERIACEAE. 



2. Frond differentiated into root, stem and branches, the latter of 

 very varied form; reproduction unknown. 



5. CAULERPACEAE. 



2. Frond filiform, branching ; not differentiated as above. 3. 



3. Filaments interwoven to form fronds of definite form. 



i. CODIACEAK. 



3. Filaments branching, not interwoven. 4. 



4. Sexual reproduction by large female and small male gametes; 

 asexual reproduction unknown ; branching more or less plumose. 



2. BRYOPSIDACKAK. 



4. Sexual reproduction unknown ; branching irregular. 5. 



5. In tissues or shells of plants or animals ; asexual reproduction by 



aplanospores. 4. PHYLI.OSIPHOXACEAE. 



5. Free, marine ; asexual reproduction by large, uiulticilate zoospores. 



3. DEKI'.KSIACEAE. 



