332 



BACTERIA IN RELATION TO PLANT DISEASES. 



In 1896-1897, Smith verified Pammel's statements, extended his inoculations to cab- 

 bages and other plants, carefully illustrated the disease in color, and obtained additional 

 information respecting cultural characters of the organism. He also discovered that infec- 

 tions take place through the water-pores. This knowledge, published in June, July, August 

 and September 1897, was also summarized in a Farmer's Bulletin issued January 8, 1898, 

 and widely distributed among cabbage-growers. Subsequently (February and March 1898) 

 Russell, and Russell & Harding, went over the whole ground in papers of considerable length, 

 confirming in the main the statements of Pammel and of Smith, and making various addi- 

 tional observations. The same year, after many additional experiments, Smith again 

 published in "Zeitschrift fur Pflanzenkrankheiten. " 



In 1 899-1 900, Harding demonstrated the disease to be common in Europe. European 

 investigators (van Hall in 1900 and Hecke in 1901-1902) were then moved to study this 

 disease. Hecke in particular did a very thorough piece of work on kohlrabi, adding con- 

 siderably to our knowledge and at the same time confirming many statements made by 

 Smith, Russell, Harding and others. 



In 1901, in his dispute with Fischer, Smith published a series of photomicrographs 

 illustrating this disease. In 1903 he published another series of photomicrographs showing 

 the effect of the black rot on turnips. 



In 1903, Potter reported on the occurrence of this disease in England, especially in Swedes. 

 In 1902-1904, Brenner, a special student of Alfred Fischer at the University of Basel, 

 went over the ground once more at Dr. Fischer's suggestion. He experimented principally 

 with cabbages, although he mentions having observed the disease in numerous other cruci- 

 fers. He added some new facts and also confirmed many statements previously made by 

 Smith and disputed by Fischer. 



In 1903-1905, Stewart & Harding, and Harding, Stewart & Prucha continued their 

 studies, the most important new facts brought out being that the organism does actually 



occur in autumn on a portion of the cabbage 

 seed grown for market in infected districts, and 

 that when cabbage-seeds are moistened with a 

 culture of Bacterium campestre it is able to live 

 on their surface for more than a year, thus ren- 

 dering it extremely probable that the disease 

 maybe disseminated by seedsmen. The manner 

 of threshing cabbage seed, as they point out, is 

 such that the dust from a few infected plants 

 would be likely to contaminate the seeds of 

 many sound plants, if not that of the whole crop. 

 In 1 904-1 905, Smith and Swingle showed that the organism could be destroyed in great 

 part by repeated freezings with liquid air and with salt and ice. The few bacteria which 

 survive the freezings are still infectious. 



In 1910, Harding summarized his studies on about 45 isolations of this organism in 

 accordance with the requirements of the Descriptive Chart of the Society of American 

 Bacteriologists. 



*Fig. I30a. 



*FiG. 1300 Left: Margin of cabbage leaf showing extrusion of fluid from the water-pores. Right: Early 

 stage of bacterial infection on cabbage leaf by way of the water-pores. 



