288 THE BANANA 



A section of a plant in the incipient stages of this disease 

 presents quite a different appearance. Small dots and 

 irregular lines of a yellowish or light-brown colour are to 

 be seen, either distributed evenly over the whole cut 

 surface or more frequently arranged in a band. Sometimes 

 they are localized in one or more patches. These dots 

 and threads are discoloured vascular bundles, and in later 

 stages of the disease they become more numerous, their 

 colour ranging from reddish to reddish-brown. At a quite 

 advanced stage of the disease the vascular bundles change 

 in colour from reddish-brown to purple or even black. 

 Secondary rots have set in by this time, and as these rots 

 are occasionally putrefactive, a disagreeable odour is 

 sometimes given off. 



Unmistakable evidence of the disease may be found 

 also in the roots. Blackened roots close to the bulb, 

 and extending into its diseased portion, are frequently 

 found. This condition has been proved to be due to the 

 organism causing the disease. 



CAUSE OF THE DISEASE 



This causal organism is a fungus, to which the name 

 Fusarium cubense has been given. It is a typical member 

 of the genus Fusarium, and exhibits near relationship to 

 other species, notably F. vasinfectum. On account of its 

 constant association with the disease the ability of 

 F. cubense to cause the wilt has been assumed for some 

 time. Dr. Brandes seems to have proved most convinc- 

 ingly, by a series of experiments which he records, that 

 there is no doubt any longer that F. cubense is the 

 cause of the Panama or wilt disease of bananas. 



There are good grounds for assuming that the fungus 

 excretes substances that are poisonous to many plants. 

 It would seem, for instance, from the results of an experi- 

 ment with cotton seedlings, that these are liable to infec- 

 tion and destruction when planted in soil heavily infested 

 with the causal organisms of the Panama disease. 



