1914) 
SCHRAMM—GRASS-GREEN ALGJE AND ELEMENTARY NITROGEN 165 
same holds true for this alga in nature seemed probable to 
Kossowitsch, who found that it grew vigorously only so long 
as а nitrate was present. He further observed that after growth 
had ceased in any culture, it was promptly resumed upon the 
addition of a nitrate solution, but not when the nitrogen-free 
nutrient solution was added. Similar cultures were started in 
which the inoculation material was either a mixture of alge 
and bacteria derived from soil or lime, or à mixture of soil bac- 
teria with a pure culture of Cystococcus. In each case the cul- 
tures were set up with and without dextrose. Table gives the 
results of these experiments. 
TABLE I 
RESULTS OF KOSSOWITSCH'S EXPERIMENTS WITH PURE AND MIXED CULTURES 
Mg. of N in cultures 
+ or — Sugar Content of cultures 
Initial Final 
— Cystococcus (pure culture) 2.6 rd 
РЕ 2.6 2.7 
— Cystococcus, Phormidium, soil bacteria, 2.6 7.1 
-- moulds 2.6 9.5 
— Pure Cystococcus culture and bacteria 2.6 3.1 
- 2.6 8.1 
— Stichococcus and bacteria 2.6 2.3 
4+ 2.6 2.7 
-— Nostoc, large round alga, Scenedesmus, 2.6 ? 
-- soil bacteria 2.6 19.1 
-- Nostoc, а Cylindrospermum (small 2.6 8.8 
-- form), soil bacteria 2.6 25.4 
Cystococcus, in pure culture, was again unable to fix free 
gaseous nitrogen, and the same conclusion is reached by Kosso- 
witsch for Stichococcus, which even in the presence of a mixture 
of bacteria failed to fix elementary nitrogen. Of especial in- 
terest are the cultures of pure Cystococcus with bacteria, as in 
these the fixation is ascribable only to the bacteria. Which 
of the organisms in the remaining cultures are responsible for 
