342 



BACTERIA IN RELATION TO PLANT DISEASES 



The new varieties are also cataloged by one of the growers, and of these 7 are marked 

 as much subject and 6 as very resistant, while 3 1 do not fall into either class. 



Wakker states that most of the leaf -infections are usually observed in the fields in the 

 month of May, but thinks that infection must take place at least a month earlier. The 

 writer's experiments have led him to the same conclusion. Undoubtedly the bulk of the 

 field infections occurs during blooming time, when insects would be visiting the blossoms 

 freely. 



The downward movement of the disease in the leaves is very slow (Wakker, Smith) . 



Fig. ]35*. 



Fig. 134.* 



MORBID ANATOMY. 



There are no hyperplasias in connection with this disease. It is primarily, and to a 

 considerable extent during its whole progress, a disease of the vascular bundles. The 

 reasons for this the writer has attempted to set forth in his papers on this organism (see 

 Literature) . They are noted briefly under the next head. The xylem portion of the bundle 

 is the first part to be attacked, especially the spiral vessels which are soon filled entirely 

 by the rapid multiphcation of the organism (plate 20, fig. 6) . This is what causes the bright 



*Fio. 134.— Cross-section of base of a hyacinth bulb, showing cavities in parenchyma due to Bad, hyacinlhi. 

 Upper part of drawing is extreme base of a bulb scale; lower is part of plateau. Starch grains are represented in 

 outline only. Slide 502 A — A3, from plant No. 67 inoculated in the flowers (see Bull. 26, p. 30). 



*FiG. 13.5. — Bad. hyacinthi: A detail from fig. 134 at X. 



