PLATE XXXI 

 Azotobacter chroococcum 



Fig. I. — Vital-stained preparation 37 days old. 



Fig. 2. — An i8-hour-old culture stained by the Guignard stain, showing strongly 

 dyed protoplasmic granules. 



Fig. 3. — A 65-hour-old cultiu-e stained by the Guignard method. 



Fig. 4. — A 9-day-old culture stained by the Guignard method. The cytoplasmic 

 matrix is here distinctly visible. 



Fig. 5. — A 65-hotu--old cultiu-e stained progressively by the Heidenhain method 

 showing some empty sheaths of the peculiar zooglea masses detected by Beijerinck 

 and Krzemieniewsky. The partition walls are visible. 



Fig. 6. — An i8-hour-old culture on mannit agar, showing the life cycle of the 

 organism. Stained by the Guignard method. 



Fig. 7. — An 18-hour-old culture on mannit agar, showing the life cycle of the 

 organism. Stained with methylene blue, i to 1,000. 



Fig. 8 and 8a. — Cells drawn from an 18-hour-old cultiu-e on mannit agar. Stained 

 by the Guignard method. 



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