THE BROWN ROT OF SOLANACEAE : MORPHOLOGY 193 



absence of endospores (heat, spore stains), bipolar staining (us- 

 ing methylene blue), Gram's stain, acid-fast stain. Presence or 

 absence of involution forms. 



Cultural Characters. Behavior in nutrient agar (shape of 

 surface colonies, color in various lightings) and in gelatin (thin- 

 sown plates) ; streaks and stabs in agar and in gelatin (Fig. 135) ; 

 growth and color on steamed potato (keep several weeks); 

 behavior in bouillon; nitrate bouillon; Cohn's solution; Uschin- 



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FIG. 136. Cross-section of young Virginia potato tuber showing that starch 

 has been removed from the vascular region occupied by Bacterium solanacearum . 

 This was done by the potato plant, not by the schizomycete. Surface unruptured . 

 Tuber invaded through the vascular system of the rhizome. No fungi present. 



sky's solution; milk, which should be kept 10 weeks (how soon 

 can you see your pencil, or read coarse print behind a tube of 

 such milk?). Watch carefully to be sure that the clearing is not 

 due to precipitation of the casein. When the milk has cleared 

 to your satisfaction add some drops of strong hydrochloric acid. 

 How do you explain the result? Behavior in lavender-colored, 

 cream-free litmus milk (which should become and remain blue; 

 watch closely to be sure that no acid is formed). Now add 

 ammonia water, drop by drop, very gradually to check tubes of 



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