THE PESTS AND DISEASES OF THE CANE 



159 



Fig. 54 



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 Sniut.^ Ustilago sacchaH (Rabenhorst). — Soris atris ; sporis ghbosis 

 subangulatis, S-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. ® 06 

 The causal organism occurs on • 

 grasses and on wild cane, which may ^ 

 be a source of infection. Butler^^ 

 has observed that those canes which 

 more nearly approach the wild va- 

 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. 



Para.sitic on sugar cane, clogging the vascular bundles w-ith 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 -f 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 

 flagellum ; occasional verj' 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. 21-^ 3332523. 



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

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

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

 to England Berkeley observed the presence of gum, and of a fimgus Lahrella sp. 

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

 terium. All of Cobb's deductions were afterwards confirmed by Eiwin Smith. ^^ 

 The manifestations of the disease have also been described by Boname®^ 

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

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

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



with an offensive slime 

 ;^^«fe^^ ^nd the growth is 



seriously affected. Va- 

 rieties differ much in 

 susceptibility. Gmn- 

 mosis of the cane was 

 earh' observed in Java 

 in connection with the 



-^ *'''■' „ sereh disease (q.v.). 



Fig. 55 , , . . ^^. '' 



but the opmion of all 



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



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



he had definiteh' established the identity of the two diseases, finding the 



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



