56 



BACTERIA IN RELATION TO PLANT DISEASES. 



Water-pore Infections. Early in 1897, by plunging healthy leaves into water con- 

 taining the bacteria, the writer obtained numerous infections of the cabbage by way of 

 the water-pores using Bacterium campestre, and later drew attention specifically to the 

 whole subject of stomatal infection (September 1907), which had hitherto belonged only 

 to the domain of speculation. A little later, as a result of field observations, he pointed out 

 (January 1898), that a large proportion of the natural infections in cabbage and similar 

 plants takes place through the water-pores, which are groups of modified stomata situated 

 on the leaf-serratures. These field observations were made in Michigan, Wisconsin, Ohio, 

 and Western New York. They covered a period of several weeks of active work in cabbage- 



Fig. 10.* 

 plantations aggregating hundreds of acres, and during this time the writer saw thousands 

 of plants in all stages of the disease. These statements respecting infection by way of the 

 water-pores were disputed in 1899, by Dr. Fischer on a priori grounds and were still held by 

 him to be doubtful in 1903, but on Long Island, where this disease prevails extensively, 

 the writer had opportunity for additional observations in 1902 and sees no reason for chang- 

 ing his statements in any way. He also obtained the disease in 1904, through water-pore 

 infections of the cabbage by spraying upon the plants young agar cultures of Bacterium 



*Fig. 10. Cabbage-plant No. 400 inoculated Dec. 9, 1904. by spraying. Photographed Jan. n. Central leaves 

 have grown since inoculation and rue free from infection, while nearly entire margin of older leaves is destroyed as 

 a result of water-pore infections. This plant belongs to the same series as that shown on plate 2 For details from the 

 margin of one of these leaves, see fig. 9. 



