ROOT DISEASES 133 



clearing affords unmistakable examples of the association 

 between the diseased trees and forest stumps and sometimes 

 these are very striking, as when the infection of a group of five 

 or six trees can be traced to the spreading roots of a single large 

 stump. In many cases the connection has been traced in detail 

 and newly diseased roots found in contact with infested roots of 

 the forest trees. 



Relatively few trees are lost in the first three or four years 

 after planting. This is in part due to the time taken (a) by the 

 fungus to develop on and about the stumps ; {b) by the roots of 

 the planted trees to grow out into the infested area, and (c) by 

 the fungus to kill a tree after infection. But observation shows 

 that when the period of heavy losses ensues, most of the trees 

 are infected from one another, so that the characteristic distribu- 

 tion of the disease is in scattered patches, the number of which is 

 very small compared with that of the stumps and logs in the 

 clearing. 



There is every reason to believe, and experience in other 

 countries agrees, that the number of species of forest trees of 

 which the stumps are readily infested by the fungus is quite 

 limited, and that the presence of the stumps of these especially 

 susceptible trees in clearings has a good deal to do with the ap- 

 pearance of the disease. It is a well-known fact that there is 

 such a special susceptibility in the case of certain cultivated 

 and semi-cultivated trees. Accurate information as to the 

 identity of the forest trees most concerned is difficult to 

 obtain. In Dominica the largest number of cases occur in 

 connection with Chataigniers {Sloanea spp.), while Mahoe cochon 

 {Sterculia caribaa), Mahoe piment {Daphnopsis tinifolia) and 

 bois cabrit or goatwood {AlgipJtila martinicensis) are also recorded 

 as susceptible. 



The disease does not develop in clearings made on poor and 

 shallow soils, or on land which remains in a swampy unaerated 

 condition. 



Occurrence in Established Plantations. 



In lime plantations no examples have been met with of the 

 persistence or recurrence of Rosellinia disease after the disappear- 

 ance of the remains of the forest growth from the soil. In cacao 

 plantations, and probably the same applies to those of coffee, 

 the disease is liable to occur in fields of any age. The liability 

 is greater in degree according to the rainfall and humidity of the 

 situation and is also affected by the kind and condition of the 

 accessory trees in the cultivation. 



There is usually no evidence of the disease having persisted 

 from the time of the original clearing, which in many cacao 

 estates is a remote one. Its occurrence seems spontaneous and 

 is mostly unexpected. In a few cases it has seemed to start on 

 the cacao trees themselves, but much more usually it has its 



