252 Early Studies in Bacterial Plant Diseases 



that the potato scab was frequently disseminated by seed potatoes, 

 and in such cases could be controlled very satisfactorily by soaking 

 the infected seed potatoes in a solution of corrosive sublimate. 

 This treatment is, however, not successful in case the fungus is 

 already present in the soil." By 1897 Arthur announced formalin 

 as a remedy against potato scab. Soon thereafter BoUey discovered 

 the fungicidal value of formaldehyde and advocated its use against 

 smut in oats.^* 



During the early 1890's so many studies of various plant dis- 

 eases were being made at agricultural experiment stations over 

 the nation that workers began to specialize in different types of 

 investigation. The bacterial disease of cucumbers, cantaloupes, 

 and squashes provided Smith with his speciality. In July 1893 he 

 had photographed the disease through four stages in cucumber 

 plants located on a hill in Anacostia in the District of Columbia. 

 In August, when reading his paper before Section G, he had given 

 the results of his histological and anatomical examinations: the 

 disease's beginning in the leaf blade; the bacillus' entrance into 

 the stem through the spiral vessels; the organism's destructive 

 action believed to be mostly confined to the phloem part of the 

 bundle, the spiral and larger netted and pitted vessels filling with 

 bacilli, and the formation of cavities filled with bacilli in the 

 tissue around the spiral vessels. He had announced these and 

 his major conclusion that the sudden wilting is due to the filling 

 of the vessels and stopping of the plant's water current. Pure 

 culture infections as yet had not been secured, and positive proof 

 that the disease is transmitted by insects had not yet been 

 established. 



He had brought the " cucumber germ " on potato from Wash- 

 ington to test in his father's garden whether the germ would 

 blight squash. A card-board memorandum indicates that several 

 hypotheses were in his mind. Some were " not tried," and some 

 yielded "' doubtful " conclusions, while to others the answers 

 was a final " no." His purpose seems to have been to test the 

 range of susceptibility among various crops and further to study 

 the areas of infection and the time required and mode of action 



" See, Fifty years of pathology, op. cit., 27. Also, Bull. Ind. Exp't Sta. 65, and 

 unpublished memorandum by Arthur, already cited. See also, H. H. Whetzel, 

 Outl. Hist, of Phytopath., op. cit., 105-106. 



