472 SCIENCE PROGRESS. 



the protoplasmic lining of the cells is very thin and the 

 large sap cavity abundantly stored with sugar. The fact 

 that the joints first showing signs of disease are not the 

 lowest and oldest may be explained by the greater ex- 

 posure of the higher ones (12th or 13th, according to 

 observations of the author), which are consequently more 

 freely tunnelled by the moth-borer, and thus bared for the 

 fungus spores. There is a small step between such cells 

 and those actually dead, and in New South Wales the 

 rind-fungus appears principally to attack canes near the 

 point of death. ^ 



The apparent periodicity observed in sereh seems to be 

 due to a different cause. The disease makes its appear- 

 ance shortly after the rains, because the stricken canes alone 

 refuse to shoot up. The rains again bring about the 

 appearance of the swarms of wawalan in Java, awakening 

 them from their summer sleep. It has frequently been 

 noticed that plant canes and ratoons (second growths from 

 the cut plants, the roots being left in the ground) are 

 differently attacked by disease. The "plants" seem to be 

 more severely affected by gumming and rind-fungus, a 

 fact which may depend on the older and stronger root 

 system of ratoons. On the other hand, in sereh the disease 

 appears to increase steadily all through the life of the plant, 

 being much more severe among ratoons. As a result of 

 this, while ratooning is to be encouraged in places attacked 

 by rind-fungus, it has practically disappeared from Java. 



12. One of the most interesting features in the study 

 of cane diseases is the apparent immunity of certain 

 varieties. Taken broadly, the " soft "' canes are the ones 

 most liable to disease, while the "hard" canes are more or 

 less resistant. It is not likely that the juiciness of the 

 stem or the hardness of the "rind" is of itself a direct 

 factor in the matter, but it is fair to infer that these char- 

 acters are amongr a series of correlated ones which render 

 the plant a more or less easy prey, just as we are told 

 white chickens are more liable to gapes and white verbenas 

 to mildew.- The Clieribon cane is especially subject to 

 1 Cobb. 2 Oarwin. 



