84 BACTERIA IN RELATION TO PLANT DISEASES. 



May 22. Pot marked : 



1 . Both sprouts sound ; but one much larger than the other. 



2. One sprout sound, one top-rot. 



3. One sprout sound, one top-rot. 



4. Both sprouts sound. 



5. One sprout sound, one top-rot. 



6. Both sprouts sound. 



7. One sprout sound; in the other the leaves are beginning to dry up. 



Pots Nos. 3 and 4 were more closely examined; in both, the young leaves above the vegetation 

 point appeared brown and dead, but the latter itself was not attacked. 

 On June 1 6 the condition of the remaining sprouts was as follows : 



Pot marked : 



1. One sprout sound; the other dead at the top, but the older leaves still living. 



2. One sprout sound; the other dead at the top, but the other leaves still living. 



3. One sprout sound; the other is cut off. 



4. One sprout sound; the other is dead. 



5. One sprout sound; the other is cut off. 



6. Two sound sprouts. 



7. One sprout sound; the other dead at the top; the older leaves still living. 



On June 20 a closer examination took place; of the infected sprout from pot No. i the young 

 leaves within the sprout are brown and dead. The vegetation point is still sound. 

 Of the infected sprout from pot No. 2, as above. 



Of both sprouts from pot No. 6, one is attacked by a borer, the other sound. 

 Of the infected sprout from pot No. 7, as i and 2. 

 Not one of the three top-rot sprouts diffused any odor on cutting. 



These are all the experiments Wakker was able to make and certainly they are not very 

 conclusive. That he had Bact. vascularum seems to me extremely doubtful. His final 

 summary is as follows: 



It seems to me that in the top-rot we have a disease which is not in the strictest sense of the word 

 parasitical, but is brought about rather by a combination of circumstances. 



Of these circumstances I mention in the first place great moistness of the air and high water con- 

 tent of the plant. That I ascribe a great influence to this rests chiefly on the observation that the 

 top-rot in East Java occurs in the rainy season, while in the dry time it is not observed. 



In the second place I believe that the tops which by the above-named circumstances are predis- 

 posed to become diseased, need to this end in addition only that the very youngest, still wholly rolled 

 up and not visible leaves do, from one cause or other, wholly or partly die off. One cause to be 

 assigned for this, in the first place, is a sudden rapid growth which is the result of the occurrence of 

 rain upon cane that has long suffered from want of water. This might then have as a result a crack- 

 ing and deformation of leaves and leaf-sheaths, the phenomena known as Pokkah-bong. Top-rot 

 would then result through the decay of the malformed leaf-sheaths and in young sprouts the Heart- 

 disease. 



Whether this theory is correct, later investigations will have to show. That the top can be killed 

 by rotting substances is proved by test iv. 



Although it follows from the above considerations that the top-rot is probably not infectious, I 

 nevertheless deem it desirable to advise cutting off and burning the affected tops. Cutting off in cases 

 of Pokkah-bong, I think, I must not advise as yet. 



Should the symptom repeat itself on a large scale, then the planting of the more sensitive varieties 

 would have to be abandoned. Concerning this, however, there is nothing now to be said. 



LITERATURE. 



1898. WAKKER, J. H. Het Top-rot in "Die Zickten van het Suikerriet op Java, die niet door Dieren veroorzaakt 

 worden. " Leiden, 1898, pp. 64-75, i plates. 



