1915] 



WESTERDIJK PHYTOPATHOLOGY IN THE TROPICS 



311 



altitudes. It is very remarkable that in the tropics tubers are 

 never, so far as I observed, affected. This fact might help 

 us to discover the cause of the difference in susceptibility 

 of the tubers of different potato varieties in our climate. 



Speaking of potatoes, I wish to point out another disease of 

 oui regions which I found in the tropics and which has the 

 greatest influence upon tropical potato culture. I am speak- 

 ing of the internal brown spot, the nature of which has not 

 been recognized. Nearly every potato tuber shows this 

 disease and in a much more striking way than in the tem- 



perate 



regions. 



The brown spot is accompanied by a soft 



_ •_ ^ -i • /^ 1 • T ^ 



consistency of the tuber and a small amount of solid sub- 

 tance. As far as we know to-day, this trouble is a physiologi- 

 cal one, caused by particular conditions of "climate and 8011,' ' 

 the nature of which is unknown to us. The cause of the disease 

 may be different in the tropics and in our regions, but a care- 

 ful study of it in warm climates might give us an indication 

 as to what conditions favor it. 



Among the large group of rust-fungi, there is only one 

 representative which is of importance to tropical agriculture. 

 This is the coffee-leaf disease, due to Hemileia vastatrix, a 

 rust which to a considerable degree ruined a large part of the 

 coffee culture of Eastern Asia, and obliged the growers to 

 introduce other species, which, unhappily, are of poorer 

 quality. On other cultural plants, however, no rust of any 

 importance occurs. The important cereal crop of the tropics, 

 tne rice, has no rust enemy. The rust of the sugar-cane is of 



no consequence in cane growing 



The same is true of the 



smut diseases. Rice smut is found exceptionally, and smut 

 of sugar-cane is a rarity; smut of corn is even rarer than in 

 our regions. 



Leaf spot diseases, belong 



ascogenous 



4V 



gi 



) 



much less frequent than in Euro 



• imperfect 

 the United 



States. The leaf spots of suga 

 Cercospora Sacchari, and C 



haeria Sacch 



Koph 



are 



dely 



spread but have little influence on cane production. They are 

 of more importance in the moist western part of Java than 

 in the drier east. The tea blights (Pestalozzia palmarum and 



