4 BACTERIA IN RELATION TO PLANT DISEASES. 
THE DISEASE. 
The line between disease and health is sometimes a very narrow one, especially 
when nothing more is involved than some slight change in function. ‘The difference, 
however, is very striking in many of the diseases here considered. The writer has 
used the word “disease”? in the common acceptation of the term, meaning thereby 
Fig. 1.* 
any marked deviation from the normal functions or structure of the plant as it now 
exists, whether wild or greatly modified by cultivation. In a sense, such a change 
as has taken place in the cauliflower, the normal flower-shoots of which have become 
*Fic. 1—Cross-section of the upper part of a sweet-corn stem parasitized by Bacterium Stewarti 
(Erw. Sm.). The location of the bacteria is indicated by black shading. Most of the affected bun- 
dles are on the periphery. The bacteria have not escaped into the parenchyma. Jamaica, Long 
Island, N. Y., July 16, 1902. The section was taken several feet from the ground, but the stem in- 
fection undoubtedly took place through one or more of the lower nodes. Drawn from photomicro- 
graph of a section stained with carbol-fuchsin. Exactly similar sections, but with a larger number 
of infected bundles, have been cut from stems of sweet-corn plants infected by the writer in August, 
1902, during the seedling stage shown in fig. 73. 
a 
a 
ee 
— 
