422 
Journal of Agricultural Research vd. xxm, no. 6 
putidum Lehm. et Neum.). The fluorescence, when it appeared, was 
mostly weak and apparently was favored by a slightly acid reaction (as 
is the case with the typical A. agile), while ammonia, contrary to the 
usual behavior of Bacterium fluorescens , remained without effect. 
The yellow rod developed from the dwarfed growth of Azotobacter agile 
retained most of the cultural characteristics of its origin; merely the 
cell form was at least temporarily very much like that of Bacterium puti¬ 
dum, and there was a clear tendency, especially in broth cultures, to 
assume endosporulation, which, however, could not be fully stabilized in 
this case. 
Quite different from the white rods of Azotobacter chroococcum, as well 
as of A. agile, are the two strains received from Dr. Mulvania (No. 26 
and 27). Both produced large amounts of gas and displayed in every 
respect the cultural characters of Aerobacter (Coli-Aerogenes group). 
However, their tendency to make large Azotobacterlike cells was very 
marked, and therefore we did not feel justified to discard them lightly 
as “contaminations.” Undoubtedly they do not belong to the life cycle 
of A. chroococcum or A. agile; but, as Mulvania (36), too, noticed gas 
formation in his Azotobacter cultures, there remains the possibility, or 
even the probability, that another species of Azotobacter exists, which 
should be more thoroughly studied. The upgrowth from the gonidia to 
large cells was very similar to that observed with other Azotobacter 
strains (fig. 10 on PI. 1). The tendency to assimilate free nitrogen has 
been ascertained with several members of the Aerobacter group (24, p. 
688 ). 
6 .—SMAU, SPORUI,ATlNG RODS 
Aztobacter vitreum did not produce any sporulating rods, but 18 strains 
were grown from A. chroococcum, A . Beijerinckii, and A. agile . They 
again proved to be polymorphous, and equally so with both Azotobacter 
species. Width and length of the rods, as well as the endospore forma¬ 
tion, varied considerably, and the cultural features proved to be equally 
unstable. But these alterations were by no means erratic; in fact, there 
was a gradual increase in the size of the rods, a progressive change from 
polar to central sporulation, and a simultaneous passing from weak to 
vigorous growth. The smallest rods with polar spores were extremely 
fragile and little inclined to grow on the substrates used. Frequently 
reinoculation became necessary, and still losses occurred. On the other 
hand, when left undisturbed on the same substrate they remained alive 
for long periods. Two of these strains first appeared in old stock cultures 
(26), and several of them survived when kept for five years in mannite 
solutions. When tested at the end of this period in beef broth and in 
mannite-nitrate solution those of A. chroococcum and A. Beijerinckii 
grew only in the latter, while those of A. agile preferred the beef broth. 
Morphologically as well as culturally these small, weakly growing, 
Gram-negative rods with polar spores are practically identical with 
Bacillus terminalis Mig., as described by Lawrence and Ford (10). At 
first it seemed as if those of the chroococcum type could be clearly 
differentiated from the agile type by the appearance of the spores; the 
latter showing ridges similar to those of B. asterosporus (A. Meyer) Mig. 
But the cultural character was distinctly different from that of B . astero¬ 
sporus and very similar to that of the other strains. Ford and his 
collaborators have seen similar ridges occasionally upon the spores of 
B. brevis Mig., B. fusiformis A. M. et Gottheil, and of related forms. 
