THE GREEN ALGAE OF NORTH AMERICA 385 



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

 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. Klebahu, 1899, divides 

 >S. annulina into two species, 5". crassi septa (Heinrich) Klebahn, 

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

 diam., 500-1200 /A long, oospores 11-19 /" diam., including mem- 

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

 jections ; the latter with cells 42-65X250-1400 p., oospores 13-26 

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

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

 varieties of 6". annulina, is hardly certain ; in the former case it 

 would not seem that the name of 5". annulina should be given 

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

 are of the crassisepta type. 



Order VI. SIPHONALES. 



v 



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 OK SIPHONALES. 



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



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



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. CODJACEAK. 



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. BRYOPSIDACEAK. 



4. Sexual reproduction unknown ; branching irregular. 5. 



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



aplanospores. 4- PHYLLOSII-HONACKAE. 



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



3. DERBESIACEAE. 



