I IO 



FUNGOUS DISEASES OF PLANTS 



of cultivated and wild cruciferous plants (such as mustard and 

 charlock) are also known to be susceptible. 



The organism, morphology and reactions. Upon gaining entrance 

 through the water pores upon the margins of leaves this organism 

 multiplies enormously. It is probable that a cellulose enzyme is 

 slowly secreted, for in time masses of bacteria cause the progress- 

 ive disappearance of the cell wall in contact with them. Through 

 the vessels of the fibrovascular bundles they make most rapid ad- 

 vances. Affected bundles are indeed usually chambered pure cul- 

 tures of this organism, and poured plate cultures, with proper 

 precautions, show a remarkable purity. Upon cutting such affected 



FIG. 25. A AND , VASCULAR BUNDLES FROM TURNIP ROOT, SHOWING FORMA- 

 TION OF BACTERIAL CAVITY ; C, THE BACTERIA. (After Erw. F. Smith) 



bundles the organism may ooze out in yellow droplets. In time 

 practically any tissue of the host may be softened and disorganized 

 (Fig. 25, A and B\ 



The organism is a short rod, with a rather long flagellum (Fig. 

 25 C). It is but slightly longer than broad in the tissues of the host, 

 yet in artificial culture it may be several times as long as broad, 

 measuring 0.7-3.0 x 0.4-0. 5/<t. It is actively motile when young 

 and nonmotile with age. It is commonly single or in pairs, and 

 no spores have been found. It responds readily to stains. 



It grows well in slightly alkaline bouillon, developing turbidity 

 and a yellow precipitate. Gelatin is gradually liquefied, complete in 

 fifteen days at 17 to 19 C., with yellow precipitate. On feebly 



