684 Journal of Agricultural Research voi.vi.No.is 



More complete studies, of course, will fill all places now vacant in the 

 table. The rather irregularly observed types G, H, J, and M are of no 

 fundamental importance in the life cycle of B. azotobacter, and our interest 

 has not been especially centered upon them. The large forms (types A, 

 B, and L), as well as the small ones (types E and F), have been found in 

 all cases. The same holds true concerning types D and I. This means 

 that the full life cycle typical for B. azotobacter has been observed with 

 every strain. That budding forms (type K) were also noticed in 23 out 

 of 24 cases is of minor interest, because this is another type which repre- 

 sents no essential link in the cycle of bacterial life. Merely its unusual 

 and heretofore nearly unknown appearance naturally attracted our 

 attention. 



The growth of the gonidia which causes this "budding" occasionally 

 leads to three other kinds of development which deserve some short 

 discussion. If the "buds" stretch out considerably, they cause the 

 formation of branched bacteria, which can be found in the Azotobacter 

 group, as well as in all other groups of bacteria. If, however, several 

 gonidia, inclosed in the same cell or in its liberated granular content, 

 start growing simultaneously in different directions, starlike forms re- 

 sult, which are frequently found in cultures of rodlike bacteria. Bad. 

 radiobacter probably is the best known example of this special type of 

 growth. But we have already reserved for a later publication good pic- 

 tures of starlike outgrowths of slender rods from the typical large globular 

 Azotobacter forms. An interesting crownlike form, representing the 

 medium stage between simple budding and the formation of stars, is 

 shown in figure 16 (PI. C) directly above the upper symplasm. The 

 third kind of gonidial development is another heretofore unknown 

 type of growth. The budding gonidia sometimes develop into forms 

 which clearly show the morphological and physiological character of 

 typical endospores. Since they are produced, however, outside of the 

 cell, they may be called exospores. In figure 20 (PI. D) different stages 

 of their development are reproduced. Their occurrence is not quite so 

 surprising as it may seem to be at first, when considered in the light of 

 the two following facts. Those "granules" which precede the formation 

 of the normal endospores inside the bacterial cells are actually nothing 

 else than small gonidia. When budding, the gonidia frequently develop 

 into thick-walled regenerative bodies, which not only germinate in the 

 same manner as endospores but may also acquire quite a considerable 

 resistance against heat. As mentioned above, regenerative bodies grow- 

 ing out of the symplasm sometimes convert themselves practically 

 entirely into spores. Budding exospores therefore are merely a special 

 application of a general rule; they are regenerative bodies with the char- 

 acter of spores. 



Normal heat-resistant enaospores showing polar germination have 

 been found in 13 of our Azotobacter cultures — that is, in more than 50 



