2 BACTERIA IN RELATION TO PLANT DISEASES. 
Since the above paragraphs were written S. F. Edwards has reported (1908) that the 
Houser cabbage “‘is practically immune to black-rot under field-conditions.”” Even when 
pure cultures of the bacteria were inoculated into the cabbage the inoculations were either 
without result or the disease advanced so slowly as to do but little injury. 
The period of incubation is variable. Hecke, inoculating by needle-puncture, obtained 
the first signs of the disease in from 7 to 28 days on leaves, and in from 9 to 31 days on stems. 
He made 33 inoculations on kohlrabi leaves by needle-puncture, every one of which was 
successful; he likewise inoculated 23 kohlrabi plants in the stem by needle-puncture, and 
Fig. 110.* 
of the whole number there was not one which did not give some indications of disease. 
Exclusive of sprays, plunge-experiments, and the use of insects, etc., almost all of my own 
inoculations were made by needle-puncture without hypodermic injection, and the first 
distinct signs of disease were generally visible in 14 to 21 days. Brenner also found this 
period of incubation correct for most of the plants he experimented with. On cotyledons, 
however, he obtained signs of the disease in 8 days, and the entire plants soon contracted 
the disease and were destroyed or greatly injured. 
*F1G. 110.—Cross-section of a cauliflower-petiole showing bacterial cavity in a small bundle (lower one at left in 
fig. 109) due to presence of Bacterium campestre. From a pure culture inoculation. A paraffin section stained with 
carbol-fuchsin. Enlarged from a photomicrograph. 
