COBB'S DISEASE OF SUGAR-CANE. 



49 



According to Cobb, an excess of moisture seems to favor the development of this dis- 

 ease. The conditions below Maclean, on the Clarence River (New South Wales), where the 

 disease is very prevalent, differ from those above Maclean, where the disease is rare, in the 

 following ways: There is a greater rainfall down the river; the banks of the river are lower; 

 the surface drainage is not rapid ; and the nearly impervious clayey subsoil is within a few 

 feet of the surface. He says also : 



In the diseased fields it is apparent that the better drained parts suffer less than the others, 

 though all the conditions except this one of drainage are the same. 





Fig. 19.* 

 THE RED STAIN. 



In 1904, R. Greig Smith investigated the red vascular bundles of gummed cane and 

 reached the conclusion that the stain must be due to the symbiotic action of an undeter- 

 mined pycnidia-bearing fungus and a white slime-producing bacillus, named by him 



*Fic. 19. Bacterium vascularum in stem of sugar-cane received in 1902 from New South Wales. The figure repre- 

 sents a bundle in cross-section. The ground tissue, endodermal sheath, and phloem are still free, also a part of the 

 xylem, including the two big pitted vessels. Sectioned from paraffine and stained with Flemming's triple stain, the 

 contrast being not exaggerated. Slide 121 (9. 



