Feb. io, 1923 
Life History of Azotobacter 
419 
Mannite-nitrate solution gave mostly only very little growth; it showed slight 
turbidity and some yellow sediment; in a few cases the solution itself became dis¬ 
tinctly yellow. 
Nitrogen fixation was not noticeable in pure cultures, but a very pronounced 
stimulating effect was exerted upon the formation of thick floating membranes in 
mixed cultures (with large spore-free as well as with fungoid cells). 
Identical transparent and yellow strains of the dwarfed growth were 
isolated from Azotobacter chroococcum , A. Beijerinckii , A. agile , and A . 
vitreum . The two atypical cultures of red pigmentation came from one 
strain of A. Beijerinckii , while two other strains of this kind did not 
produce such growth. It can be safely said, therefore, that the various 
Azotobacter species and varieties did not exhibit any difference in their 
dwarfed growth. Bacterium antityphosum Almquist, discussed in Part I 
(25, p. 147), is equally indistinguishable from our dwarfed Azotobacter 
growth morphologically as well as culturally; only the agglutination test 
would permit differentiation. Furthermore, one culture of Bacillus 
pumilus gave us a very similar, although very weak growth, and it is to 
be expected that in many other cases analogous results will be obtained, 
as soon as the bacterial gonidia and their behavior will be made the object 
of adequate studies. 
4. FUNGOID GROWTH 
As was discussed above, this type of growth is closely connected with 
the gonidial development. But whereas the gonidia, when they grow 
as such, become similar to a minute yellow Mycobacterium, the fungoid 
cells in the majority of cases grew as a white, fairly large Mycobacterium, 
which displays on potato a very characteristic dry, raised growth of pink 
color. Here the differentiation of Azotobacter chroococcum and A. Bei¬ 
jerinckii from A. agile and A. vitreum is very sharp. Identical strains 
of the white-pink mycobacterium were isolated from practically all our 
cultures of A . chroococcum and A. Beijerinckii , but never from A . agile 
or A. vitreum . A few mycobacterium cultures of yellow or orange color 
were branched off in both cases, but these were always closely connected 
with the yellow dwarfed growth common to all Azotobacter strains. 
According to the descriptions given by Lehmann and Neumann {18 ), 
Sohngen (4/), and Vierling (45), our yellow cultures may be identified 
with Mycobacterium luteum Sohngen, and the orange ones with Myco¬ 
bacterium lacticola Lehm. et Neum.; but we have also to confirm Vier- 
ling’s findings that the pigmentation is not absolutely stable. Changes 
between yellow and orange were observed and occasionally also a tem¬ 
porary loss of pigmentation—that is, the same instabilities as were found 
with the dwarfed growth. 
The white-pink fungoid growth, characteristic of Azotobacter chroococcum 
and A. Beijerinckii , is perhaps identical with Mycobacterium album 
Sohngen. But the description given by the Dutch author (41) is too short 
to permit a definite statement. As no other description of this type of 
growth seems to have been published, our notes may find a place here. 
Morphology (Pl. 4).—Pale, irregular, slimy sheaths with dark granules are most 
common on mannite-nitrate agar and in mannite-nitrate solution. They are usually 
the first outgrowth of the symplasm and assume gradually more regular shape and stain 
more uniformly. On beef agar and in beef broth the pleomorphism typical of Mycobac¬ 
terium is always noticeable. Figures VI and XII of Table 69 and Figure X of Table 
70 in Lehmann’s and Neumann’s atlas (18) could have been made from our slides. 
In milk especially richly branched forms were seen; but continued cultivation in milk 
eaused the transformation into slime producing small rods. . On potato the inclination 
to assume endosporulation was very pronounced, while cultivation on potato agar gave 
either small nonsporulating rods or white or yellow coccoid growth. In soil and in 
