428 
Journal of Agricultural Research 
Vol. XXIII. No. 6 
life histories follow the same fundamental lines can no longer be denied, 
provided that the facts recorded in the literature are taken under ade¬ 
quate consideration. In morphological, as well as in physiological respects, 
much interesting information is to be expected from such investigations. 
As was frequently noticed in bacteriological tests of soils, wherein 
usually a normal growth of Azotobacter is to be observed, this organism 
may be temporarily replaced by other nitrogen-fixing bacteria, such as 
Bacterium lactis viscosum and other nonsporulating rods, various large 
sporulating bacilli, some micrococci, etc. The possibility that different 
developmental stages of the same organism may have to be made respon¬ 
sible for such changes sheds new light upon the very great ability of the 
bacteria to adapt themselves to widely varying environmental condi¬ 
tions. It is especially noteworthy that the life cycle of Azotobacter not 
only unites several of the best-known aerobic nitrogen- and nitrate- 
assimilating organisms, but also strong ammonia producers and forms 
which are known to be very able to make use of the various organic 
substances of the soil, first of all of the humates, namely, several myco¬ 
bacteria (41, 43). 
SUMMARY 
Tests made with 30 strains of Azotobacter and with several cultures of 
related bacteria have shown that only two species of Azotobacter are 
completely characterized thus far: Azotobacter chroococcum and A. agile 
Beij. (syn. A. Vinelandii J. G. Lipman). A. Beijerinckii J. G. Lipman 
is a variety of A. chroococcum and A. vitreum Lohnis is probably a variety 
of A. agile. A. Smyrnii C .B. Lipman et Burgess can not be accepted as 
a species; according to all marks ascribed to it by its authors it is the 
large sporulating growth type of A. chroococcum . A. Hilgardi C. B. 
Lipman and A. Woodstownii J. G. Lipman are both incompletely described 
and should not be retained. 
The genus Azotobacter is characterized by the morphological and 
physiological behavior of its seven different cell types. These are 
(1) large nonsporulating globular, oval, or rodlike cells of white, yellowish, 
or brown color, with polar or peritrichous flagella, able to act as gonidangia 
and microcysts; (2) coccoid cells of white, yellow, or pink pigmentation, 
the vegetative growth of the regenerative bodies, identical with Micro¬ 
coccus concentricus Zimm., Micrococcus sulfureus Zimm. emend. Lehm. et 
Neum., and with Microcococcus roseus (Bumm) Lehm et Neum., respec¬ 
tively; (3) dwarfed cell type of yellow, white, or of red color, the vege¬ 
tative growth of the gonidia; (4) irregular, fungoid cells, producing a 
yellow, orange, or (in the case of A. chroococcum and A. Beijerinckii) a 
white or pink growth; the former two are closely related to the dwarfed 
growth and identical with Mycobacterium luteum Sohngen and with 
Mycobacterium lacticola Lehm. et Neum., respectively, while the latter is 
probably identical with Mycobacterium album Sohngen; (5) small non¬ 
sporulating rods of white or of yellow color, the former being identical 
with Bacterium lactis viscosum (Adametz) Lehm. et Neum. in the case 
of A. chroococcum and A. Beijerinckii t but with Bacterium putidum 
(Fliigge) Lehm. et Neum. in the case of A. agile and A. vitreum; (6) small 
sporulating rods, identical with Bacillus terminalis Mig., Bacillus fusi - 
formis A. M. et Gottheil, and in the case of A. chroococcum and A. Bei¬ 
jerinckii with Bacillus pumilus A. M. et Gottheil; (7) large sporulating 
cells, growing white, yellow, and brown, identical with Bacillus luteus 
Baker et Smith, Bacillus petasites A. M. et Gottheil, Bacillus malabarensis 
