7 6 



BACTERIA IN RELATION TO PLANT DISEASES. 



The writer lias 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 only for the briefest periods. The degree of cold 



Fig. 63.* 



is governed 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 

 more ice is added. Under the most favorable circumstances the temperature of the 



*Fic. 63. Modification of the Ostwald water -bath used by the writer for thermal death-point 

 experiments. This consists of a porcelain-lined pot n 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 

 Ki irdliurf; burm-r and is controlled by Roux's thermo-regulator. Murrill's gas-pressure regulator 

 is shown at the left. 



