78 BACTERIA IN RELATION TO PLANT DISEASES. 



Still [generally] it is a fact which everyone can easily prove that really the roots of a Sereh-dis- 

 eased plant consist of short stubs with decayed ends. * * * 



I believe that precisely in the red stripes of the nodes, which, as already remarked, are filled with 

 gum, we must notice the symptom of the injurious results of the insufficient water-supply on the part 

 of the varieties of cane that are sensitive to it, and the absence of such stripes proves then that the 



variety is not so sensitive to a scant water-supply as to experience injurious consequences therefrom. 



* * * 



It is naturally possible that^ as in the hyacinths, so in the grape-vine, both a gum-disease and a 

 bacterial disease may occur, and this also may be the case in sugar-cane, if, for example, top-rot 

 should prove to be a disease actually caused by bacteria ; but certain it is that gum originates in sugar- 

 cane in connection with all injurious influences affecting the plant, in roots, leaves and stems by 

 wounding, without co-operation of parasites, as well as by diseases. * * * 



The assumption that the gum-formation in the plant may be promoted by a chronic lack of water 

 is a theory, like any other, which by several utterances in literature is made plausible, and is further 

 sustained by the fact to which attention has thus far not been called, that it is in the nodes that the red 

 stripes appear, that is, where the evaporation of the leaves must make itself most felt. * * * 



I further assume that that influence which has been operative during the formation of the buds 

 [lack of sufficient water] makes itself felt in such a way that the plants which spring from those buds 

 are weaker than plants developed from buds under more favorable circumstances. * * * 



An internally weaker plant will react on lack of water sooner than a normal one ; that is to say in 

 substance, the gum-formation will be stronger and the vessels will become more obstructed. * * * 



That we may thus come to the traditional "bouquet" Sereh-plant with sprouted roots on the 

 stem and dead roots in the ground is clear. * * * 



The sprouting buds on the stem present a greater difficulty. Before discussing it, I want to 

 recall that not a single one of the earlier theories has led to an explanation of it. * * * 



If this presentation is right, and there is much to be said for it, then it may be accepted that the 

 Cheribon cane as a variety had some years before entered upon the period of senility and that this 



manifested itself in great sensitiveness to lack of water with the consequent gum-formation, etc. 



* * * 



Wakker also cites the nitration test of Janse as showing further that the Sereh disease 

 stands in very close connection with lack of water. 



He says it is a fact also that on the borders of the plantations close to the drains where 

 the sugar-cane roots have only three directions in which to grow, instead of four, and are, fur- 

 thermore, subject to drying-out, there the worst Sereh-plants are met with. 



He accounts for the spread of the disease from west to east by the fact that the disease 

 first appeared in the Cheribon cane, which itself originated in the west, and that the eastward 

 spread does not indicate the movement of a parasite, but rather a more general distribution 

 of the particular variety of cane subject to the disease. 



The becoming Sereh-diseased of some imported varieties that are Sereh-free in their own country 

 can be explained by the aforesaid influences as well as by assuming the theory of infectiousness. * * * 



Finally, the immunity of some sugar-cane varieties rests either on the possession of a more vig- 

 orous root-system, or on a lesser sensitiveness to lack of water, so that gum-formation does not take 

 place nor the obstruction of the vessels. * * * 



With former writers, I consider the red stripes in the nodes as a most clearly discernible char- 

 acteristic of the beginning of the disease. * * * 



Recently Greig Smith has ascribed a red string disease of sugar-cane to a bacillus (B. 

 pseudarabinus) . (See Cobb's Disease, p. 49.) 



Soltwedel and Prinsen-Geerligs are authority for the occurrence of Sereh in Malacca, and 

 Kobus is authority for its occurrence in Borneo and Bangka. 



In his criticism of Wakker 's theory Kriiger states that Tylenchus sacchari Soltwedel is a 

 typical sugar-cane parasite not uncommon in Java. 



The last communication on the subject the writer has seen is by Zeijlstra. According 

 to him, two factors are necessary for the production of Sereh, receptivity and a parasite. 

 He says in so many words: 



My observations lead me therefore to the following two theses : 



1 . Sugar-cane is a double race, variable in receptivity for the attack of the " Sereh "-disease. 



2. The "Sereh "-disease is an infectious disease, the cause of which up to this time is unknown. 



