Feb. io, 1923 
Life History of Azotobacter 
409 
positive results had been obtained (25, p. 62-64). Figure 80 deserves 
special attention because it illustrates a mode of fission which has been 
observed by very few authors and which thus far has never been photo¬ 
graphed. Large round bodies appear, which later split on their diameter, 
beginning in the center, into two large, comma-shaped bacilli so char¬ 
acteristic of B. Megalerium and related “species.” As was said in Part 
I (25, p . 125, 126 ), Schroen has described this occurrence more than 30 
years ago, and at the same time 33 . Klein and Dowdeswell made analogous 
observations with Vibrio cholerae. The small non-sporulating rod forms 
of Azotobacter seem to act occasionally in a similar manner. In figure 
55 on Plate 5 an intact globule is visible and also several pairs of slightly 
curved, plump rods, of which especially those located near the upper 
edge of the photograph are very suggestive. Figure 84 on Plate 7 illus¬ 
trates the return to the normal large spore-free cells (after passage of the 
symplastic stage). In potato cultures this reversion occurred most fre¬ 
quently. The cells shown in figure 79 and 81 to 83 are related to repro¬ 
ductive processes; they represent various types of gonidangia and 
sporangia. 
2.—different modes of reproduction 
All types of bacterial reproductive organs have been found with Azoto¬ 
bacter—namely, gonidia and gonidangia, regenerative bodies (zygo¬ 
spores, etc.), arthrospores, microcysts, endospores, and exospores. It 
was pointed out in Part I (25, p. 119-143) that all these organs of repro¬ 
duction are fundamentally not so different as might be assumed. As 
the pleomorphism of the vegetative bacterial cells finds its explanation 
in the varying participation of nuclear material and of other cell elements 
in cell construction, so also in the various modes of reproduction nuclear 
substances always play the dominant r 61 e, supported to a smaller or 
larger extent by reserve material, cell membrane, etc. When the nuclear 
material is accompanied by very little other cell elements, gonidia are 
produced. More reserve material and a more or less durable membrane 
characterize the regenerative bodies and arthrospores. When the whole 
cell assumes a globular or oval shape and thickens its membrane a micro¬ 
cyst results, while the contraction of most of the cell content and the 
formation of an exceptionally tough membrane leads to the formation of 
an endospore, or of an exospore if the growing spore buds out of the 
mother cell. Gonidia and regenerative bodies may multiply as such, 
producing the dwarfed and the coccoid growths discussed above; arthro¬ 
spores and microcysts, endospores and’ exospores are true resting forms, 
although a secondary transformation to regenerative bodies or to gonidia 
was also observed repeatedly with these types of reproductive organs. 
While bacteria of the usual small dimensions as a rule form only one to 
two to four gonidia in each cell, the larger cells, for which the term goni¬ 
dangia was introduced in Part I (25, p . 121) may contain a much larger 
number or in their place two to three or more endospores; in the latter 
case the gonidangium becomes a true “sporangium.” 
Figures 85 to 87 on Plate 8 demonstrate formation and liberation of 
the gonidia by normal large globular Azotobacter cells, while figure 
77 Plate 7 illustrates the analogous process with the large threads 
of the large sporulating type. A comparison of figures 86 and 87 shows 
how either (in the latter case) the nuclear material practically alone 
may persist and give rise to the dwarfed growth discussed above, or 
(in the former case) how other cell elements may participate in the 
