45 



produced to effect defoliation. So far this abnormal leaf -fall has not 

 been recorded, or at any rate I have not seen any cases of it, in this 

 country. 



The leaves of nursery plants are attacked by several fungi but 

 none of them are serious and I do not consider it necessary to 

 describe them in detail here. 



Two fungi are commonly found on leaves which turn brown or 

 yellow at the edges, Gleosporium alho-rvhrum and Phyllosticta 

 ramicola. These will l)e referred to later in considering stem 

 diseases. They do not cause serious diseases of the leaves. 



Cephaleuros sp. 



This alga which is found commonly on the under sides of leaves 

 where it produces small brown spots has no economic importance. 

 The " red rust " of tea, a serious disease in India, is caused by a 

 similar Cephaleuros. It is worth noticing in passing that such 

 an alga has been found penetrating the leaf tissue of Hevea as most 

 diseases associated with the tea plant are also common to Hevea. 



No leaf diseases have any economic importance. Fortunately, 

 no fungus belonging to the family JJredinese has been found on 

 Hevea leaves. It is to this family that Hemileia vastatrix, the 

 cause of the well-known coffee leaf disease which ruined the culti- 

 vation of coffee in Ceylon, belongs. It is quite possible that a 

 member of this family jnight adapt itself to the leaf of the rubber 

 tree and might even have equally devastating effects as Hemileia in 

 Ceylon but at the present time that does not seem probable. 



The consideration of leaf diseases need not keep us any longer. 

 Owing to the particular nature of the leaf it is, perhaps, naturally 

 not particularly suitable as the host for parasitic fungi. 



DISEASES OF THE STEM. 



Of the stem diseases now recorded in this country the most 

 serious are those caused by Corticium sahnonicolor (pink disease), 

 PhytopJithora faheri (bark canker), Phytophthora species (causing 

 decay of the tapped surface) and Botryodiplodia theobromse (die-back). 



Other fungi causing disease are Phyllosticta ramicola, Gleo- 

 sporium alho-ruhrum (forerunners of die-back), Cyphella hevese 

 (thread blight) and the abnormal condition of the stem, which I 

 must include here, caused by burrs. 



Pink Disease (Corticium sahnonicolor). 

 In Java and in this country this disease is exceedingly common. 

 The disease was very fully investigated in Java by Zimmerman 

 Zehnter and Rant, and in this country by Brooks and Sharpies. 

 The literature obtainable on this subject is considerable and in 

 compiling a summaiy for purposes of discussion I must point out 

 that this literature gives a vei'y complete account of the disease. 



