6o4 BACTERIA IN RELATION TO PLANT DISEASES 



man' and later that of Jones,^ showing that bacterial pathogens may invade the host 

 tissues by dissolving the cell-wall material by enzymes, a great deal of data has ac- 

 cumulated to show that enzymic dissolution of the pectic or less frequently of the 

 cellulose materials plays a large role in the invasion of plant tissues by bacterial patho- 

 gens. Coons and Kotila^ were able to precipitate out from a culture of B. atrosepticus 

 a fraction which dissolved the pectic substances of cell walls. Further advances in this 

 field are dependent upon advances in knowledge of the physiology and chemistry of 

 enzymes. 



Casual observation and reflection upon the action of bacterial plant pathogens 

 suggests that bacteria also form or lead to the formation of toxic substances that plas- 

 molzye and necrose the cells of the host, and thus enable them to invade the tissues 

 deeper and deeper. The phytopathological literature is full of references to the role of 

 bacterial "toxins" and "toxic" substances in the attack of pathogens upon the host 

 tissues. This elevation of the principle of toxic action of pathogens to a dictum of 

 general application in the field of phytobacteriology is based on comparatively few 

 isolated experiments. Spieckerman^ describes experiments presumably carried on 

 with toxic substances, which are thermo-labile. He did not demonstrate, however, 

 that the plasmolysis noted is not associated with a resultant disruption of the tissues. 

 Laurent^ and van HalP report the demonstration of both enzymic and toxic and 

 plasmolyzing principles from cultures of micro-organisms which are doubtful plant 

 pathogens. Kotila and Coons^ report demonstration of both enzymic and toxic action 

 by B. atrosepticus. 



Smith^ contended that Bad. tumefaciens is intracellular and is carried through 

 plant tissues from primary to secondary tumors by metastases. His contention has 

 been challenged latterly by Robinson and Walkden' who contend that the bacteria 

 are intercellular and migrate through the intercellular spaces and protoxylem vessels 

 in the form of zoogleal strands, and stimulate cell division along their path, and by 

 Riker'" who contends that the organism is intercellular and is carried through the in- 

 tercellular spaces when these are suffused with cell sap, following mechanical injury, 



' Spieckerman, A.: "Beitrag zu Kenntniss der bakteriellen Wundfiiulniss der Kulturpflanzen," 

 Land-d'. Jahrb., 31, 155-78. 1902. 



= Jones, L. W.: "Pectinase, the Lytolytic Enzyme Produced by Bacillus carotovonis and Certain 

 Other Soft Rot Organisms," Vermont Agr. Exper. Sta. Bull. 147, pp. 281-360. 1910. 



^ Coons, G. H., and Kotila, J. E.: "The Transmissible Lytic Principle (Bacteriophage) in Rela- 

 tion to Plant Pathogenes," Phytopath., 15, 357-70. 1925. 



■t Spieckerman, A.: loc. cit. 



s Laurent, Emile: Recherches experimentales sur les Maladies des Plantes," Ann. de I'lnst. 

 Pasteur. 1899. 



* van Hall, C. J. J.: "Bacillus suhtilis (Ehr.) Cohn und B. vulgatus (Flugge) Mig. als Pflanzen- 

 parasiten," Centralbl.f. Bakieriol., Abt. II, 9, 642-52. 1902. 



' Kotila, J. E., and Coons, G. H. : "Investigations on the Blackleg Disease of Potato," Michigan 

 Agr. Exper. Sta. Tech. Bull. 6y. 1925. 



* Smith, E. F.: see various works cited previously. 

 'Robinson, W., and Walkden, H.: loc. cit. 



■oRiker, A. J.: "Some Relations of the Crown Gall Organism in the Host Tissue," /. Agr. Re- 

 search, 25, iig- ^2. 1923. 



