148 



BACTERIAL DISEASES OF PLANTS 



that number of minutes), and it doe:- 

 readily. Probably it is often 

 carried on some of the seeds 

 from diseased plants, and 

 whole fields may become in- 

 fected in this way, directly 

 or indirectly. ^ Once present 

 in a field, cabbage insects 

 greatly favor its distribu- 

 tion, especiall3^ by gnawing 



not lose its virulence 



Fig. 84. Fn,. s.",. 



Fig. 84. — Water-pore infections on a cabbage leaf, 2 months along. Pure- 

 culture inoculation by the writer. Bacterial movement downward in the vessels. 



Fig. 85. — Central part of a cabbage leaf showing brown venation due to 

 Bacterium campestre. The inoculation was on a leaf lower down. Bacterial move- 

 ment downward in vessels of the inoculated leaf, then upward, first in vessels of 

 the stem aii.l afterward in those of this leaf. District of Columbia, 1897. 



into diseased leaves and then crawling over healthy ones. 



' Geo. K. K. Link has reported to me verbally a case observed liy him in Southern 

 Florida on new land in the spring of 1919 where (50 per cent of 100 acres of cabbages 

 was destroyed })y this disease, the total shipments amounting to only 40 car-loads. 



