THE FUNGI WHICH CAUSE PLANT DISEASE 21 



The plant pathogens as yet known, with few exceptions, belong 

 to the two genera Pseudomonas and Bacillus between which they 

 are about equally divided. 



In the earlier days of bacteriology and to some extent in recent 

 days, bacteria have been seen in diseased plant tissues and have 

 been placed by their observers in one genus or another and cited 

 as the causes of the diseases in question but without actual evi- 

 dence that they cause the diseases and very often without any real 

 evidence as to the genus to which the bacteria belonged. It is 

 of course usually impossible to identify such forms and they must 

 be dropped from consideration. 



Coccaceae (p. 18) 



No representative of this family parasitic upon plants has yet 

 been reliably recorded in America. Micrococcus tritici Pril ^^ 

 upon wheat in England is probably in reality Bacillus prodigiosus 

 and not pathogenic. Micrococcus ph3rtophthorus Frank ^^ ^^ re- 

 ported as a cause of potato rot and also associated with potato 

 black-leg is perhaps in reality identical with Bacillus phytoph- 

 thorus Appel. Micrococcus nuclei Roze, M. imperiatoris Roze, 

 M. flavidus Roze, M. albidus Roze, M. delacourianus Roze and 

 M. pellucidus Roze are assigned by Roze ^ as the causes of va- 

 rious potato troubles in Europe, and M. popoH Del.''* is said to be 

 the cause of canker on Populus. 



Bacteriacese (p. 18) 



Bacterium Ehrenberg (p. 18) 



These non-motile forms, perhaps owing to their lack of power 

 of locomotion, are comparatively rare as plant pathogens. 



Bact. briosianum Pav. is given as the cause of rotting of to- 

 mato fruit and distortion of vegetative parts in Italy. ^^ It is 

 described also on Vanilla.^'" 



Bact. montemartinii Pav. is described as the cause of a canker 

 of Wisteria.*'^ 



Bact. mori B. & L. is said to cause leaf and branch spots on 

 mulberry.'*^ 



