I\ T. Bkooks and A. Sharplbs 



6:j 



failed to show any of the characteristic <l;nl< coloured hyphae of this 



fungus running through the vessels even in the most badly attacked 

 portions of the wood. 



Though Diplodia cacaoicola was absent, the wood was permeated 

 with hyaline hyphae. A section of the branch including the transition 

 area and a portion of the dead wood was taken and cut into numbered 

 blocks throughout its length. Razor sections of the wood at different 

 levels were made, the lower portion of the transition area being found 

 most favourable for examination. Transverse sections through this 

 part show the hyphae ramifying through the elements of the wood, 

 being especially prominent in the vessels (Fig. 1). The wood of Hevea 



Fig. 1. Transverse section of wood showing hyphae in the vessels, x 40. 



brasiliensis is mostly composed of fibrous elements together with a 

 comparatively small number of large vessels and narrow medullary 

 rays. 



A study of longitudinal sections, both radial and tangential, shows 

 the nature of the attack upon the wood. A favourable radial section 

 shows the hyphae passing transversely through the wood along the 

 medullary rays by way of which also the fungus passes from the bark 

 into the wood. The fungus obtains food from materials stored in the 

 ray cells which become filled with septate hyphae (Fig. 2). In radial 

 section the medullary rays appear to be broad bands of infected tissue 

 passing through the wood. At places where the vessels meet the 



