Algae in Some Colorado Soils. 
25 
enable certain higher plants to develop normally. Without algae, 
however, there was a comparatively slight growth of the higher 
plants. These experiments are not conclusive but they are indi¬ 
cative of the close relationship existing between algae and bacteria 
in the soil. More than that, they lead one to believe that in these 
experiments algae supplied carbohydrates for the nitrogen fixing 
bacteria which in turn furnished nitrates essential for the normal 
development of the higher plants. 
Dr. Hugo Fisher (1) speaks of the symbiosis existing between 
Azotobacter chroococcum and Oscillatoria. He is of the opinion 
that Azotobacter occurs abundantly between the algal filaments, the 
algae furnishing carbohydrates, the bacteria nitrates. Frank (2) 
found that there was an increase in the nitrogen content of a nitro¬ 
gen-poor sand on which algae developed in the light, while the same 
sand if kept in the dark did not increaes in nitrogen. Soil bacteria were 
present in both cases. Schloesing and Laurent (3), working along 
the same lines, showed that soil containing both bacteria and algae 
could fix free nitrogen in large quantities while the same soil cov¬ 
ered with quartz to prevent algal growth did not increase in nitro¬ 
gen. The above workers assumed that the algae in their mixtures 
had the power to fix free nitrogen. This assumption was later 
proven to be erroneous, at least for green algae (Chlorophyceae). 
In 1894, P. Kossowitsch (4), working with pure cultures of 
green algae, species of Cystococcus and Stichococcus t demonstrated 
that these alone could not assimilate the free nitrogen of the air. 
Later, in 1900, Kruger and Schneidewind (5), using pure cultures 
of green algae, species of Stichococcus, Chlorella and Chlorothecium, 
substantiated the results, of Kossowitsch and proved that the green 
algae they used did not have the power to fix free atmospheric 
nitrogen. It is highly probable that none of the green algae pos¬ 
sess this power. They further showed that when inorganic or 
organic nitrogen was excluded from the nutrient solution, all the 
species of algae in pure culture made no noticeable growth. There 
was abundant growth, however, when the same sub-stratum was sup¬ 
plied with combined nitrogen. In neither of the above pure cul¬ 
tures of algae was there any nitrogen fixation. But in the same 
medium, both an abundant development of algae and a fixation of 
nitrogen took place if pure cultures of the algae were inoculated 
with Azotobacter. In the latter case fixation is, of course, attrib¬ 
uted to Azotobacter, while algae furnished them .with the or¬ 
ganic matter necessary for their life. 
(1) Fisher, H., Ueber Symboise von Azotobakter mit Oscillarien. Cent. f. Bakt. Abt. II., 
Bd. XII., p. 267, 1904. 
(2) Frank, A. B., Ueber den experimentellen Nachweis der Assimilation freien Sticks- 
toffes durch erdbewohnende Algen. Berichte d. deutschen botan. Gesellschaft. Bd. VII., 
p. 5, 1889. 
(3) Schloesing and Laurent. Recherches sur la fixation de l’azote libre par les plantes, 
Annales de l’lnstitut Pasteur T. VI., p. 65 W. 824, 1892. 
(4) Kossowitsch, P., Uiitersuchungen ueber die Frage, ob die Algen freien Stickstoff 
fixieren. Botan. Zeitg., Bd. LII, p. 97, 1894. 
(5) Kruger and Schneidewind. Sind niedere, chlorophyllgrune Algen imstande, den freien 
Stickstoff zu assimilieren ? Landwirtsch. Yahrb. Bd. XXIX., p. 771 ff., 1900. 
