.w. 



'a 









:..-, . .. 



iS.#,' 







Fig. 3. Section of R. rubrion growing exponentially under strictly 

 aerobic conditions in the dark and containing only traces of photosyn- 

 thetic pigments. The membrane-bounded vesicles are extremely rare 

 in this type of cell. Arrows indicate two such vesicles. Main fixation 

 2 hours, followed by a short treatment with ribonucleasc; post stain- 

 ing with lead hydroxide. X 120,000. 



Fig. 4. Section of R. rubruniirom a culture grown aerobically in the 

 dark, and then allowed to synthesize photosynthetic pigments for 3 

 hours under semiaerobic conditions in the dark. Peripheral membrane- 

 bounded vesicles are more numerous than in cells grown strictly 

 aerobically. Compare with Fig. 3. Treatment as described for Fig. 3. 

 X 120,000. 



