130 



BACTERIA IN RELATION TO PLANT DISEASES. 



MORBID ANATOMY. 



The lesions in this disease are strikingly like those induced by other organisms of this 

 group, e. g., Bacterium hyacinthi and Bad. vascularum. The vascular system is occluded 

 by the bacteria to an astonishing degree. So far as I know, scarcely anything comparable 

 to it in extent and severity occurs in the animal body, the nearest approach, perhaps, being 

 certain septicaemias (figs. 54, 55,56). There is this astonishing difference, however, due 

 to the very different character of the circulation in plants and animals, that while in many 



cases the general septicaemias of the 

 animal body are rapidly fatal, a few 

 days sometimes sufficing, this disease 

 of maize progresses slowly in spite of 

 the presence of enormous numbers 

 of the bacteria, and destroys the 

 plant apparently only when the 

 water-conducting tissues (vascular 



Fig. 56.* 



bundles) have become blocked up by the invading organism to such an extent that 

 transpiration greatly exceeds water-supply. An early death as the result of the action 



*FlG. 56. Cross-section of an internodal bundle in sweet-corn, showing restriction of Bacterium stewarti to the 

 xylem part of the bundle. The result of a pure-culture inoculation made in the seedling stage by placing the bacteria 

 on the tips of young leaves. Material collected and fixed in October 1902. The entire stem at this level contains 287 

 vascular bundles, of which all but 10 are occupied by the bacteria. In every instance (?) the bacteria are still confined 

 to the xylem part of the bundle. Slide 248 A 6. 



fFlG. 57. Diagrammatic longitudinal section through lower half of a sweet-corn kernel attacked by Bacterium 

 stewarti, the areas occupied by the bacteria being drawn in solid black (lower left-hand side) . S, envelope of the grain ; 

 St. starchy part; E, scutcllum; P, plumule; R, radicle; B, base of kernel. The starchy part was very soft when 

 embedded and is squeezed together and upper part torn away. A detail from X is shown in fig. 58, A . Slide 485 (7. 

 X 14- From Golden Bantam corn grown from diseased seed in the summer of 1908. 



