THE PESTS AND DISEASES OF THE CANE 159 



Diseases of the Stem. The fungi that attack the stem form the more 

 destructive diseases of the cane, and have been more intensively studied. 

 A short account of them is appended. 



Black Smut. 8Q Ustilago sacchari (Rabenhorst) . Soris atris ; sporis globosis 

 subangulatis, 8-18, olivaceo-brunneis, vel rufescentibus, episporio crasso levi instructis. 



The appearance of infected cane and of the spores is shown in Figs. 

 53 and 54. The organism which causes the disease is found in all affected 

 parts. The top of young cane is most severely affected, and is turned to a 

 black whip-like substance covered 

 with a greasy foul-smelling slime. ^* & 

 The causal organism occurs on 

 .grasses and on wild cane, which may ^ 

 be a source of infection. Butler 69 



has observed that those canes which x 270 



more nearly approach the wild va- FIG. 54 



rieties are more susceptible, though 



the thicker tropical varieties are far from immune. Generally the damage 

 is not great, but the writer has seen no inconsiderable damage in Mauritius. 

 It has been reported from Natal, India, Java, Queensland, Mauritius and 

 British Guiana. 



Gumming Disease. Bacterium (Cobb), Pseudomonas (Smith), vascularum. 



Parasitic on sugar cane, clogging the vascular bundles with a bright yellow slime, 

 and forming cavities in the soft parenchyma ; frequently comes to the surface of the 

 inner leaf sheaths as a viscid slime. Surface colonies on + 6 standard nutrient agar pale 

 yellow, smooth, glistening, rather small, round, rather flat with sharp margins ; rods 

 small measuring on an average, 0*4 X i microns when stained ; motile, single polar 

 ilagellum ; occasional very slight liquefaction of gelatine, growth on potato cylinders, 

 good but not copious ; litmus milk is blued ; no reduction of nitrates, no acids, no 

 reduction of litmus, no gas. Group No. 2i- 3332523. 



Gumming of the cane and the disease connected therewith was first de- 

 scribed by Dranert 58 as causing a serious disease in Brazil. In the same year 

 Home 115 reported a diseased condition of canes in India, and in specimens sent 

 to England Berkeley observed the presence of gum, and of a fungus Labrella sp. 

 It was afterwards studied by Cobb 81 in Australia, who isolated the causal bac- 

 terium. All of Cobb's deductions were afterwards confirmed by Ei win Smith. 82 

 The manifestations of the disease have also been described by Boname 83 

 in Mauritius as the " maladie de la gomme." The disease is outwardly 

 characterized by the exudation of drops of gum from a cut or punctured 

 surface, as shown in Fig. 55. The top of the cane also becomes charged 



with an offensive slime 

 and the growth is 

 seriously affected. Va- 

 rieties differ much in 

 susceptibility. Gum- 

 mosis of the cane was 

 early observed in Java 

 in connection with the 



FIG sereh disease (q.v.), 



but the opinion of all 

 the earl}- pathologists in Java was that there was no causal connection between 

 the two conditions. Very recently, however, Wolzogen-Kiihr 84 stated that 

 he had^definitely established the identity of the two diseases, finding the 

 Bacillus vascularum present in all cases of sereh. The disease known in 



