196 Rhodora [NOVEMBER 
exception shown in figure 9 is rare. All the figures of this plant were 
made from material preserved in formalin and although there is 
very little shrinkage, yet there is just enough to show, in many places, 
the colorless connections between the cells. The cells are mostly 
cylindrical, usually longer than wide, and closely packed in the sheath. 
The colorless intercalary heterocysts are common (fig. 10). The 
sheath is mostly smooth, always colorless, and from two to four mi- 
crons in thickness. At the ends of hormogone-bearing branches, the 
sheath is often thickened up to twelve microns (fig. 12). The cells 
of the branches are sometimes longer than those in the main filament, 
but are often shorter. 
Filaments grow in length and develop branches by simple division 
of cells as shown in figure 9. Hormogones 37-163 microns in length 
and 8-12 microns in width occur at the ends of all branches or in short 
special branches. The cells of the hormogones are not well marked 
off from each other. Their color remains blue-green throughout 
their growth. The short hormogone-bearing branches are all vari- 
ously curved (fig. 10). 
STIGONEMA medium sp. nov. Filis liberis, inter algas varias spar- 
sis, repetite et irregulariter vel subsecundatim ramosis, 8-16 u crassis; 
ramis patentibus, filo primario plerumque tenuioribus, cylindricis vel 
clavatis; vagina 4-8 y crassa, ad apices usque ad 12 u, continua, hya- 
lina; cellulis plerumque diametro longioribus, cylindricis, uniseriatis, 
aerugineis vel fuscis; heterocystis forma et magnitudine cellulis nor- 
malibus similibus, hyalinis, intercalaribus; hormogoniis terminalibus, 
37-163 X 8-12 u, aerugineis. 
Filaments unattached, floating among other algae, repeatedly 
branched in all directions or somewhat secundly, 8-16 u diam.; 
branches patent, generally thinner than the primary filament, cylindri- 
cal or clavate; sheath 4-8 y thick, up to 12 u at the ends of the 
branches, even, hyaline; cells usually longer than their diameter, 
cylindrical, in one series, blue-green or brownish; heterocysts similar 
to ordinary cells in form and size, hyaline, intercalary; hormogonia 
terminal, 37-163 X 8-12 u, blue-green. 
Forming a minute, soft sod, among other algae, mostly blue-green, 
Chebacco Pond, Essex, Massachusetts, October, 1909. 
This plant shows characteristics of both Hapalosiphon and Stigo- 
nema. It is characteristically a Hapalosiphon from its single row of 
cylindrical cells usually longer than broad; from its method of branch- 
ing, and in that it usually has the cells in the branches longer than 
those in the main filament. It has the characteristics of a Stigonema 
in its habit of forming hormogones in the apices of the branches; in 
