io 6 FUNGOUS DISEASES OF PLANTS 



I. BACTERIACE^ 



These organisms consist of cylindrical or occasionally somewhat 

 ovoidal rod-like cells, straight or very slightly curved, never spiral. 

 Growth is by elongation of the rod, and division takes place by a 

 septum (leading to a fission) perpendicular to the direction of elon- 

 gation. Separation of the daughter cells may take place in such a 

 way that the cells may commonly be single, or united two or more 

 in a chain. Endospores are frequent, rare, or wanting, depending 

 upon the species. Motile organs (flagella) may or may not be 

 present. 



The majority of the important plant disease-producing species 

 thus far found are included in two genera, both of which possess 

 motile organs, 1 viz. Pseudomonas 2 and Bacillus. 



Pseudomonas Migula. These organisms are motile by means 

 of flagella on one pole of the cell only, the flagella varying in 

 number from I to 10, usually 1-3 (monotrichiate or lophotrichiate). 

 Endospore formation is relatively rare. 



This is a rather comprehensive genus on account of the variability 

 in the number of flagella, varying on the one hand towards Bacil- 

 lus, and on the other, when the rods are slightly curved, toward 

 Microspira of the spiral forms. Among species of special interest 

 in this connection are the following : Pseudomonas campestris 

 (Pammel) Erw. Smith, Pseudomonas Stewarti Erw. Smith, Pseudo- 

 monas Phaseoli Erw. Smith, Pseudomonas tumefaciens (Erw. Smith 

 and Townsend). Pseudomonas Olece (Arcan.) Trev., Pseudomonas 

 Hyacinthi (Wakker) Erw. Smith, Pseicdomonas vascularum (Cobb) 

 Erw. Smith, Pseudomonas Juglandis Pierce, Pseudomonas mal- 

 vacearum Erw. Smith, Pseudomonas Syringa vvxv Hall, and Pseudo- 

 monas Pruni Erw. Smith may also be mentioned. 



Bacillus Cohn (emend.). These organisms are motile by means 

 of wavy-bent flagella scattered irregularly over the cell (polytrichiate). 



1 A few species of the nonmotile genus Bacterium (Migula emend.) have been 

 described as of phytopathological interest, among which are Bacterium teutlium 

 Metcalf. (Centrbl. f. Bakt. Parasit. u. Infektionskr. 13 (II. Abt.) : 28-30. 1904; 

 also Neb. Agl. Exp. Sta. Rept. 17 : 69-112. 1904.) 



2 Smith has advanced (Bacteria in Relation to Plant Diseases, pp. 16S-171) 

 strong arguments for the substitution of Bacterium in place of Pseudomonas ; and 

 he would establish a new generic name, Aplanobacter, for the nonmotile forms 

 generally referred to Bacterium. 



