504 BACTERIAL BLIGHT OF BEANS. 



the pods the organism readily invades the young seeds, but 

 curiously enough, in examining an infected crop of Lima beans 

 recently, I found that in many cases the seeds were infected when 

 I could not find any trace of disease on the pods. How infection 

 comes about in such cases I am at a loss to know. 



Seeds which have been attacked by the blight are frequently 

 undersized, and malformed, and show one or more sunken, dis- 

 coloured areas. It seems probable that the 9Ji<janism is chiefly 

 carried over from one season to the next by means of these dis- 

 eased seeds, although there is also the possibilitv of reinfection 

 from the soil where rotation of crops is not practised. 



The Cause of the Disease. 



The organism causing the bacterial blight of beans in 

 America was described by Erwin F. Smith in 1897* as Bacillus 

 phaseoli; he isolated the organism and secured numerous infec- 

 tions with pure cultures. The disease had been previously 

 ascribed to bacteria by other writers, but the organism had not 

 been described nor had its pathogenicity been proved. 



Further studies of the cultural characters of the organism, 

 which he now named Pseudomonas Phaseoli, were published by 

 Smith in iQOi.f The same or a very similar organism has also 

 been briefly described by Delacroix,^ who obtained it from dis- 

 eased beans in fields near Paris. 



The South African Disease. 



No difficulty was experienced in isolating the organism from 

 the diseased tissues, and the same organism has been isolated 

 repeatedly from diseased leaves and seeds. 



Inoculations were carried out by atomising young growing 

 bean plants with a suspension of the culture, and the first signs 

 of infection were observed 7-10 days after infection. From the 

 leaf spots thus produced the organism was re-isolated, and 

 further successful inoculations carried out with the re-isolated 

 culture. In only one case did the controls become infected, when 

 plants were used growing out of doors in drums, and this 

 occurred during a spell of rainy weather. Subsequent experi- 

 ments were carried out in a different part of the grounds, and no 

 further infection of the control plants occurred. 



Characters of the Organism. 



The characters of the organism coincide closely with those 

 given by Smith for Bacterium phaseoli, and there can be no doubt 



* Description of Bacillus phaseoli n.sp., with remarks on related 

 species. — Proc. Am. Ass. Adv. Sci. (1897), 288-290. 



f The cultural characters of Pseudomonas Hyacinthi, P. campestris. 

 Ps. Phaseloi and Ps. Steivarti, four one flagellate yellow bacteria para- 

 sitic on plants. Division of Vc^t. Phys. and Path. Bull. No. 28 (1901). 



f'La graisse. maladie bactericnne des Haricots," Comptes Rcndus. 

 129. 656. 



