454 



Journal of Agricultural Research 



Vol. XII, No. 7 



is believed, from the activity of other species of bacteria which enter 

 the cells following invasion by Baci. tabacum. These species appear 

 always to be present in old lesions as judged by the isolation studies. 



DESCRIPTION OF BACTERIUM TABACUM 



Bacterium tabacum, emend. 



The primary cause of tobacco wildfire is a grayish white, rod-shaped 

 organism with rounded ends. It is motile by means of a single polar 



Fig. 1. — Parenchyma cells from the margin of a lesion showing Bacierium tabacum in the intercellular 



spaces and within the cells. 



flagellum which is about twice as long as the body of the bacterium 

 (fig. 2, a). Motility can be observed when fresh material is examined in 



a drop of water or when prepara- 



y ^ |k ( •tW tions are made from i8-hour-old 



A V V A f ^^N bouillon or agar cultures. Flagella 

 m { (2. 1 M ■ ^^^ f ^^^ easily demonstrated when the 

 / / / m Aw ^^^^3 organism from such cultures is sub- 

 's I ^ / JF m ^H^^ jected to the staining method out- 

 U ^ ^^ ^ fl lined by Morrey (2). The bacterium 

 ^^^^f ''^^--^ ^W usually occurs singly within the host 

 ^^ ^'^"yy^^ tissues, but in culture chains of as 

 ^^Btb ^ima^^i^mmm^ .^mmmm,u,^^B^ many as five elements have been 



noted (fig. 2, fc). The limits of size 

 vary from 2.4 to 5 by 0.9 to 1.5 \x, 

 the most common size being 3.3 by 

 1.2 /x. No involution forms have 

 been observed; neither have endospores been demonstrated. 



The organism stains readily with aqueous- and carbol-fuchsin, anilin 

 gentian-violet, and methylene blue. It is Gram-negative, however, 

 and is not acid-fast. Neither is a capsule demonstrable by the methods 

 of Rabiger or Welch. 



The organism has been cultured mainly upon glycerin agar and potato 

 agar. Colonies appear in these media on the second day in poured plates 



Fig. 2. — a, Flagella of Bacierium tabacum stained 

 by Morrey 's method; b. Bad. tabacum, from 

 bouillon stained with carbol-fuchsin, showing 

 arrangement of the elements. 



