290 THE BANANA 



that if healthy bulbs are planted on such soil they will 

 probably become infected. This leads to the considera- 

 tion of another method of distribution of the fungus 

 namely, that mud carried on the feet of men and animals, 

 or on the wheels of vehicles, may serve as a medium for 

 dissemination of the fungus for great distances. 



Insects may act as carriers, but there is no definite 

 information on this point, and probably it is of little 

 importance. 



Infected banana leaves are frequently found among 

 the " trash " used for protecting bunches when they are 

 packed for transport to the steamers. This trash is often 

 carelessly thrown about at various points along the route, 

 and has probably aided in the distribution of the fungus. 



ECOLOGY 



The severity and the spread of this disease are strikingly 

 correlated with certain well-defined weather conditions. 

 Wet weather, especially if it is characterized by driving 

 rains conducing to movement of surface water, is appar- 

 ently a factor of considerable importance in the dissemi- 

 nation of the disease - producing organism. In Porto 

 Rico, for instance, shortly after the rainy season has set 

 in, there is a decided increase in the number of apparently 

 new cases, and more rapid progress of the disease in plants 

 already infected. Laboratory experiments show that the 

 spores are very subject to injury by desiccation. Since the 

 surface of the soil becomes very hot and dry during the 

 dry season, it is unlikely that spores deposited thereon 

 would survive. Another reason may be that the young 

 fleshy roots, which are especially susceptible to infection, 

 are not developed during the dry season, but push out from 

 the rhizome in large numbers after the rains have set in. 



In arid regions, where irrigation is necessary for the 

 successful production of bananas, the disease is unknown. 

 No case has been observed in the drier districts of southern 

 Porto Rico, southern Jamaica, or northern Colombia. 



