2 Proceedings of the Royal Irish Academy. 



strongly held about that time that bacterial diseases of plants as such did not 

 really exist. That this view was entirely erroneous was, however, soon clearly 

 proved by the irrefutable evidence brought forward by E. F. Smith (26)^ ; and 

 during the years that have followed our knowledge of the bacterial diseases of 

 plants in general, and of the potato in particular, has rapidly increased. 



Under the name of rjamjrene of the stem., a disease of the potato plant 

 which had hitherto not been n&tieed there was described as occurring in 

 France, in the year 1890, by Prillieux and Delacroix (24). The disease was 

 described as being characterized liy a profound alteration of the tissues at the 

 base of the stem, which progressed from below upwards. No insects or fungi 

 could be found present to account for the trouble ; but bacteria were very 

 plentiful in the dead, brown cells. Infection experiments were carried out, 

 using as inoculating material the raw, bacteria-containing dead tissues of an 

 affected stem, and the disease was reproduced when such material was trans- 

 ferred to healthy stems. The description given of the disease and its cause is 

 a very short one, and no details are given as to the isolation of the pathogenic 

 organism in pure culture. Nevertheless, the authors believed that the disease 

 was a bacterial one ; and they gave the provisional name of Bacillus caulivorus 

 to the organism which they supposed was the cause of it. In their "Maladies 

 des Plantes Agricoles" the same authors state that this organism, when grown 

 in broth or gelatine, produces a very well-marked uranium-green colouration 

 of these media, which increases in intensity on shaking. Later on Delacroix, 

 in dealing with B. caidivorus, speaks of it as most probably identical with 

 Bacillus fluorescens liqiiefaciens Flugge, a common saprophytic form, which, he 

 suggests, may perhaps under certain special conditions become parasitic. It 

 should, however, be noted that, as far as we are aware, it has never really 

 been proved that B. caulivorus actually is pathogenic to the potato. It is not 

 sufficient merely to obtain an organism from a diseased tissue, and regard it as 

 a cause of disease; successful inoculation experiments with pure cultures 

 and the re-isolation of the same organism in pure culture from the diseased 

 tissues, can alone provide actual proof of pathogenicity. Griffon (15) has quite 

 recently stated that various investigations have made it seem probable that 

 both Bacillus fuorescens licjiiefaciens and B. fluorescens putridus may be the 

 cause of diseases in cultivated plants, he having found them associated with 

 diseased turnips and cauHiiowers. No account, however, is given of infection 

 experiments ; and, as Eiehm^ points out, the mere presence of these organisms 

 in cases of disease in plants is no proof of their pathogenic character. 



A bacterial disease of the tomato, egg-plant, and Irish potato was described 



' The numbers in brackets reter to the Bibliogiapliy at tlie end of the pajier. 

 ' Zeitachrift fiir Pdtinzeniiranltheiten xx, 1910, p. 426. 



