1913] Blanchard,— Two new Species of Stigonema 199 
larity to Hapalosiphon in that its cells are commonly nearly rectangu- 
lar; its sheath is smooth; there is a distinct tendency to unilateral 
branching; and the first cell of a branch usually projects into the 
main filament as in Hapalosiphon. S. medium shows itself distinctly 
like a Stigonema in its repeated branching; in the fact that the branches 
do not taper in the least and are often slightly clavate; and in the fact 
that hormogones are formed in abundance in all the branches. It also 
differs from the Hapalosiphon in having the cells of the branches often 
shorter than those of the main filament. It therefore seems necessary 
to put these three genera together as subgenera of the genus Stigo- 
nema, and let Sirosiphon be the subgenus comprising those forms 
now known as Stigonema. Thus:— 
Genus, Stigonema Agardh. 
1. Subgenus Sirosiphon Bornet & Flahault. 
2. Subgenus Hapalosiphon (Niigeli) subg. nov. 
Nägeli ex Bornet € Flahault, Revision des Nostocacées 
Heterocystées, part 3, p. 54, 1887, as genus. 
3. Subgenus Fischerella Bornet & Flahault. 
Acknowledgement is due to Mr. Frank S. Collins for loan of books 
and assistance by suggestion, to Mr. Charles Bullard for loan of her- 
barium specimens, and to Dr. F. D. Lambert for material and assis- 
tance. 
BIBLIOGRAPHY. 
Bornet and Flahault: Revision des Nostocacées Heterocystées; part 3: 1887. 
West, G. S.: British Freshwater Algae, Cambridge, 1904. 
Kirehner, O., in Engler and Prantl, Naturliche Pflanzenfamilien, Teil 1. 
Abt. 1a, 1898. 
Tilden: Minnesota Algae, vol. I, 1910. 
Wolle: Fresh Water Algae of the United States, 1887. 
Wood: A contribution to the history of the Fresh Water Algae of N. A., 1872. 
Forti: Sylloge Myxophycearum, 1907. 
EXPLANATION OF PLATE 105. 
Magnification: Figures 1 to 8, X 280; 9 to 12, x 420. 
Figures 1 to 8 inclusive are Stigonema anomalum. 
The beginning of a branch. 
Young branch and intercalary heterocyst. 
Primary filament with short hormogone-bearing branches, unilater- 
ally arranged. Lateral heterocysts and vacuolated cells. 
Escaping hormogones. 
Escaping hormogone. 
A branch after escape of hormogone. 
Hormogones. 
Formalin material showing connections between cells. 
PURA ote 
