194 



BACTERIAL DISEASES OF PLANTS 



plain milk with shaking and compare the reaction with old milk 

 cultures of Bacterium solanacearum. Then neutralize, and some- 

 what more, with hydrochloric acid and observe the second result. 

 In view also of the bluing of litmus milk what do you conclude 

 as to the probable cause of the slow clearing of the milk cultures? 

 Distil old milk cultures and test steam for presence of ammonia. 

 Test in peptone water in properly made fermentation tubes with 

 various sugars and alcohols (compare with No. XII). Can you 



Fig. 137. — Longitudinal section through an inoculated potato stem showing 

 the red stained dense mass of Bacterium solanacearum restricted to a single spiral 

 vessel. X 170 circa. 



obtain growth in the closed end with any carbon food? (Read 

 what is said in " Bacteria in Relation to Plant Diseases," Vol. I, 

 pp. 53-54, respecting good and bad fermentation tubes). If you 

 have time study the nitrogen nutrition of the organism. Can it 

 use asparagin? Salts of ammonia? Try Meyer's mineral solu- 

 tion: a, with ammonium citrate; 6, with ammonium lactate. It 

 should grow abundantly in a, and not at all in h. Can you find the 

 cream-splitting form? The writer knows it only from Sumatra. 



