cobb's disease op sugar-cane 



15 



SIGNS OF THE DISEASE. 



The most conspicuous signs of this disease are dwarfing, striping of the leaves, dying 

 of the tops, decay of the heart (terminal bud), and the appearance of a yellow slime or 

 gum in the bundles of the stem and leaves. Many of the bundles are also stained red. 

 Microscopic examination shows that this gum contains millions of bacteria. Cobb and 

 Boname agree that there is also a reduction of the sugar-content. 



Fig. 4.* Fig. 5.f 



The disease is primarily one of the vascular system, but in advanced stages the paren- 

 chyma is attacked, especially the soft tissues just below the terminal bud, and cavities are 

 formed which are filled with the yellow bacterial slime. Sometimes these cavities contain 

 as much as a teaspoonful of the slime (fig. 4). In the later stages of the disease, the 



*Fig. 4. Rot of sugar-cane clue to Cobb's disease (Bacterium vascularum). Longitudinal section through the 

 upper part of stem of plant No. 6 just under terminal bud, showing a closed bacterial cavity which was filled with 

 yellow slime (bacteria). Enlarged 3 times. 



tFic 5. Radial longitudinal section through a leaf-sheath of sugar-cane from inoculated plant No. 4, showing 

 general occupation of the intercellular spaces by bacteria, which are oozing to the surface through stomata, 2 months 

 from date of inoculation, and several feet from places inoculated (see text). Outer face of sheath at left. Section 

 taken between vascular bundles which are filled with the bacteria. For condition of bundles in sheath as shown on 

 cross-section, see fig. 7. Drawn with Abbe camera, Zeiss 3 mm. 1. 40 n. a. apochromatic objective, and No. 2 compen- 

 sating ocular. Slide 466 H 9. For a detail at x, see fig. 6. 



