404 
Journal of Agricultural Research voi. xxm, no. 6 
A. vitreum Lohnis (Laboratory Number 9). 
A. sp. (Laboratory Numbers 26 and 27). 
Cultures No. 1 to 11 are identical with those studied in 1914 (26) with 
the exception of No. 7b and 7c, two strains of Azotobacter agile recently 
received from Krai's Museum in Vienna (A. Vinelandii Lipman-Ambroz 
and A. agilis Dahlem). No. 12 and 13 are old stock cultures of the 
Laboratory of Soil Bacteriology. No. 14 to 16 and 16c were received from 
Dr. J. G. Lipman, New Brunswick, N. J.; No. 16b, 17, and 20 are sub¬ 
cultures of No. 112, 141, and 522 of the New York Museum of Natural 
History. No. 18 and 19 were received from Prof. D. H. Jones, Guelph, 
Ontario, in 1912 (his strains 1 and 3). No. 21 to 25 are new isolations 
obtained in the spring of 1916 from soil samples received from Dr. C. B. 
Lipman, Berkeley, Calif. No. 26 and 27 were sent to us by Dr. M. Mul- 
vania, Knoxville, Tenn. 
Fifteen of these strains (No. 7, 9, 10 to 14, 16, 16c, 18, 21 to 25) grew 
as typical large nonsporulating cells, when the investigations were started ,* 
4 cultures showed only large sporulating cells (No. 2, 3, 4, and 7b), 2 
small sporulating rods (No. 5 and 6), and 3 irregular fungoid cells (No. 15, 
17, and 19); 4 were made up of small nonsporulating rods (No. 7c, 16b, 
26, and 27), 1 of coccoids (No. 20), and 1 of dwarfed cells (No. 1). Al¬ 
though it was known in only some of the cases where atypical growth 
occurred that this was not due to contamination, we decided to include 
all atypical strains in our studies and to base our ultimate decision upon 
the outcome of these experiments. 
Each of the 30 Azotobacter strains was tested in about 100 to 200 and 
sometimes more transfers. Each transfer was subjected to 4 to 6, but 
occasionally to many more microscopic tests. The results presented in 
this paper are therefore based on over 20,000 observations. Numerous 
additional tests were made with cultures of several other “species," 
which proved to be identical with the newly evolved growth types of 
Azotobacter—namely Bacillus petasites A.M. et Gottheil, Bacillus inala - 
barensis Lohnis et Pillai, Bacillus danicus Lohnis et Westermann, Bacillus 
pumilus A.M. et Gottheil, Bacillus Freudenreichii (Miquel) Mig., Bacillus 
fusiformis A.M. et Gottheil, and Bacterium lactis viscosum (Adametz) 
Lehm. et Neum. Some of these cultures were kept in the senior 
author's collection; others were obtained from New York or from Vienna. 
LIFE CYCLE OF AZOTOBACTER 
In Figure 1 of our preliminary paper ( 28 ) we gave a schematic sketch 
of the various cell types and modes of reproduction of Azotobacter. Four 
types or subcycles of growth were considered to be most characteristic. 
The more thorough study of the problem, however, led to the discovery 
that from every Azotobacter culture not less than seven different growth 
types can be developed and stabilized; all of them are interchangeable. 
The cells characterizing these seven types of growth are the following 
(the letters in parentheses referring to the designations used in our pre¬ 
liminary paper) : 
Large non-sporulating cells (types A, B, La, Ka, and J). 
Coccoid forms (type I). 
Dwarfed cell type (types Ea, Ej 3 , and Kc). 
Fungoid cell type (types G and Ky). 
Small non-sporulating rods (type Fa). 
Small sporulating rods (type F/ 3 ). 
Large sporulating cells (types L, M, and KX). 
