606 RUBBER 



apparently healthy cortex; they are pale yellowish-brown, 

 sometimes continuous for several inches, but often inter- 

 rupted here and there to form a netted or perforated 

 plate. If a cambium is developed round such a brown 

 sheet a plate of wood is produced. These plates are 

 distinguished from those introduced from small nuclei by 

 their enormous extension as compared with their thick- 

 ness. They may be 2 or 3 ft. in length, while only about 

 J in. thick. 



The cores of wood which form the bulk of the nodule 

 vary, according to the size of the latter, from spheres the 

 size of a pea to roughly spherical lumps about 4 in. in 

 diameter, or plates up to 4 or 5 ft. long and i ft. in 

 breadth, which completely cover one side of the stem. 

 The cortex which overlies large nodules usually splits. 

 On badly affected trees a crop of small nodules is 

 frequently found surrounding the old. 



Nodules are easily removable in their early stages. 

 They are then embedded in the cortex, and shell out 

 readily, leaving a layer of laticiferous tissue overlying the 

 main wood of the stem. The removal of large nodules 

 usually entails the destruction of this underlying lati- 

 ciferous tissue and the consequent production of a large 

 open wound. 



The cause of these nodules has not yet been ascertained. 

 They have been attributed to dormant buds, injuries 

 caused by carts, etc., and previous attacks of canker, 

 none of which theories can, if true, have any but a very 

 limited application. In the vast majority of cases there 

 is no evidence of anything of the kind. Bateson has 

 recently announced that the brown cells include latex 

 tubes, and this has been confirmed by Mr. G. Bryce, who 

 is now investigating this problem in Ceylon. It is hoped 

 that the investigations now in progress will throw further 

 light on the subject. 



Another phenomenon which has not yet been traced 

 to fungus agency is the decay of the tapped cortex; that 

 is, the thin layer of original cortex which is left overlying 

 the cambium. This decay occurs in wet weather, usually 

 in the North-east Monsoon, October-November. It is 

 especially common on trees which are tapped for the first 



