Jan., 1921] 
WANN — FIXATION OF FREE NITROGEN 
29 
Krzemieniewska, H. Der Einfluss der Mineralbestandteile der Nahrlosung auf die 
Entwicklung des Azotobakters. Bull. Intern. Acad. Sci. Cracovie, CI. Math, et 
Nat. 1910: 376-413. 1910. 
Krzemieniewski, S. Untersuchungen iiber Azotobacter chroococcum Beij. Bull. Intern. 
Acad. Sci. Cracovie, CI. Math, et Nat. 1908: 929-1051. 1908. 
Lipman, J. G. Experiments on the transformation and fixation of nitrogen by bacteria. 
New Jersey Agric. Exp. Sta. Rept. 24: 217-285. 1903. 
. Report of soil chemist and bacteriologist. Azotobacter studies. N. J. Agric. 
Exp. Sta. Rept. 26: 254-280. 1905. 
MoUiard, M. L'azote libre et les plantes superieures. Rev. Gen. Bot. 28: 225-250. 1916. 
Remy, T., and Rosing, G. Uber die biologische Reizwirkung natiirlicher Humusstoffe. 
Centralbl. Bakt. II. 30: 349-384. 191 1. 
Schramm, J. R. A contribution to our knowledge of the relation of certain species of 
grass-green algae to elementary nitrogen. Ann. Mo. Bot. Gard. i: 157-184. 
1914 (a). 
: Some pure culture methods in the algae. Ann. Mo. Bot. Gard. i: 23-45. 1914 (b). 
EXPLANATION OF PLATE I 
Fig. I. The complete apparatus of the 1917-18 experiment. The ten series are 
connected, on the right, by T-tubes, forming a single complete series for the purpose of 
aeration. 
Fig. 2. The complete apparatus of the 1919 experiment, occupying a bench in the 
greenhouse. The series in the foreground is no. 6A (urea, with glucose), on which a very 
vigorous growth was produced by all species except no. 7 (Protococcus sp.); the fourth 
and fifth flasks from the right of the series were inoculated with this species. The check 
flasks (7th, 14th, and last from the left) stand out clearly because of the absence of growth 
in them. 
