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 man}- 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 



*FiG. I. Cross-section of the upper part of a sweet-corn stem parasitized by Bacterium Stnvarti 

 (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 token several feet from ithe ground, but the stem in- 

 fection undoubtedly took place Uhrough one or more of the dower nodes. Drawn from photomicro- 

 graph of a section stained with carbol-fuohsin. 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. 



