1914) 
SCHRAMM—GRASS-GREEN ALGJE AND ELEMENTARY NITROGEN 171 
tion that the contaminating fungus in pure culture was unable 
to fix free nitrogen, led the author to the conclusion that the 
Nostoc is, in all probability, directly responsible for the free- 
nitrogen fixation. Further, he would place Azotobacter in close 
relationship with the Chroococcacee, a family in which, he sug- 
gests, some forms capable of fixing free atmospheric nitrogen 
may be found. 
Richter (29), working with pure cultures of Nitzschia palea 
and Navicula minuscula, reached the conclusion that the former, 
and probably the latter also, is unable to assimilate elementary 
nitrogen in the absence of combined nitrogen. Heinze (15), 
in experimenting with a Nostoc culture which he had purified 
until it contained as a contamination only a Streptothrix, found 
that in solutions free from combined nitrogen and sugar but 
containing respectively mono, di, and tripotassium phosphate, 
a clearly demonstrable amount of free atmospheric nitrogen 
was fixed. Тһе Streptothrix was subsequently isolated and tested 
as to its ability to fix elementary nitrogen, both with and with- 
out sugar, but always with negative results. In conclusion, 
Heinze reasserts his former belief that Nostoc is capable of fixing 
elementary nitrogen. 
Mameli and Polacci (22) succeeded in growing Oedogonium, 
Spirogyra, Zygnema, and Protococcus in nutrient solutions free 
from combined nitrogen, and demonstrated by analysis an 
increase in total nitrogen. They ascribed to these forms, and 
to chlorophyllous cells in general, the faculty of synthesizing 
ammonia from free nitrogen and nascent hydrogen. Pure cul- 
tures were not used. Boresch (3) found that Phormidium 
corium Cohn became brown when grown in solutions containing 
very small amounts of combined nitrogen, but that the green 
color reappeared following the addition of potassium nitrate 
or organic nitrogen compounds. Several species of Oscilla- 
toria, Rivularia, and Chroococcus behaved similarly. But 
Anabena sp. did not change color even when the solution in 
which it was growing had become completely exhausted of its 
combined nitrogen. While the investigation concerns itself 
primarily with the relation of nitrogen to the color in alge, 
the observations point once more to species of Anabena as pos- 
sibly belonging to the class of free-nitrogen-fixing organisms, and 
