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 ver^- striking in many of the diseases here considered. The writer has 

 used the word "disease" in the common acceptation of the term, meaning thereby 



any marked deviation from the normal functions or structure of the plant as it irow 

 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-scclion of the upper part of a s\vcet-coni stem parasitized by i?at-/(.')-i;(Ht 5'/i'ii'(7r/( 

 (Erw. Sm.), The location of the 'bacteria is indicated by black shading. Most of the aff-ected bun- 

 dles are on tlie periphery. The bacteria have not escaped into tire parenchyma. Jamaica, Long 

 Island, N. Y., July i6, 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 oarbol-fuohsin. Exactly similar sections, but with a larger number 

 of infected bundles, have been cut from stems of sweet-icorn plants infected by the writer in August, 

 1902, during the seedling stage gliown in fig. 73. 



