'222 Some Diseases of Plantation Rubber in Malaya 



causing disease of Hevea bark. No mycologist who has resided in Malaya 

 for any considerable period has yet isolated a Phytophthora from diseased 

 rubber bark, hence the statement of Rutgers (15) of Java who after 

 a brief visit to the Federated Malay States, and without isolating the 

 supposed causative fungus, announced the presence there of a bark 

 canker caused by Phytophthora Foberi cannot be considered conclusive. 

 Until the fungus has been isolated from diseased bark and has success- 

 fully infected trees which have been inoculated it seems premature 

 to say that the bark canker caused by Phytophthora Foberi occurs in 

 Malaya. 



Rutgers and Arens (16) consider that the burrs on rubber trees are 

 often due to Phytophthora Faberi, a view for which the writer does 

 not think sufficient evidence has vet been brought forward. 



9. Burrs. 



There are two kinds of burrs on rubber trees, one consisting of 

 small, pea-like swellings in the bark, the other being irregular woody 

 growths extremely variable in size which arise both on tapped and 

 untapped surfaces though chiefly on the former. The pea-like nodules 

 can be cut out with a knife as they are somewhat easily separated from the 

 surrounding tissues. This kind of burr is of little economic importance 

 The irregularly shaped burrs on the other hand are of considerable 

 economic importance as they seriously incommode tapping operations 

 and may even render the renewed bark incapable of being tapped 

 effectively. These burrs are specially abundant on trees that weir 

 overtapped during the boom of 1910. 



Apart from Rutgers and Arens (16), mycologists are in agreement 

 that burrs on rubber trees are not due to the action of parasitic organisms 

 but are caused by some physiological disturbance. 



Bateson (3) attributes the formation of the "pea" type of burr, 

 which often occurs on the sites of old leaf scars, to the stimulus set up 

 by the coagulation of latex in the tubes which formerly passed out 

 to the leaves with the vascular bundles. Richards and Sutcliffe (13) 

 put forward the view that the large, irregular burrs are likewise caused 

 bv the stimulus on the surrounding tissues set up by the coagulation 

 of latex in tubes which belong to the laticiferous system of the stem. 

 There is good evidence for both these views. A small percentage of 

 burrs is doubtless due to wounds made in I lie wood through bad tapping. 



With the conservative and more careful methods of tapping in 



