76 



BACTERIA IN RELATION TO PLANT DISEASES. 



The writer has no very satisfactory way of making exposures for determining 

 the minimum temperature for growth. His method is to make such exposures in 

 the bottom of a large, well-filled ice-box, which is opened as little as possible during 

 the progress of the tests, and then onl)- for the briefest periods. The degree of cold 



Fig. 63.*^ 



is go\'erned by the amount of ice. A good thermometer is exposed in the midst of 

 a bundle of inoculated tubes, and if the temperature shows any tendency to rise 

 nrore ice is added, l^ nder the most favorable circumstances the temperature of the 



*FiG. 63. — Modification of the Ostwald water -l)al1i ii'sed by tlie writer for tlicnnal death-point 

 experiments. This consists of a porcelain-lined pot II inches in diameter at the top. This is filled 

 with water kept in motion by a water-wheel turned by electricity. The heat is applied by means of a 

 Friedburg burner and is controlled by Roux's thermo-regulator. iMurrill's gas-pressure regulator 

 is shown at the left. 



