62 Sphaeronema sp. 



e.g. a fresh surface exposed by tapping. Besides these, two other kinds 

 of spores are produced, one being a large, almost spherical, thick walled 

 resting spore 10-20 microns in diameter (the great majority are 10-14 

 microns in diameter) produced at the ends of short lateral branches, 

 especially on the mycelium at or near the surface (see PL IV, fig. c). 

 Cases have been observed where these spores were produced on the 

 mycelium embedded in the tissue several cells deep, and in the par- 

 ticular cases observed pycnidia were scanty or entirely absent (see 

 PL V, fig. a). 



From the experiments and field observations it would appear that 

 with a high percentage of humidity pycnidia will usually be produced 

 very quickly in large numbers, while under dry weather conditions the 

 resting spores are produced sometimes in almost equal abundance. It 

 follows of course that weather conditions cannot be relied on as an aid 

 in checking or eradicating the disease. 



Deep tapping undoubtedly aids in the thorough establishing of the 

 fungus in the tissues since under those conditions penetration to the wood 

 is quickly effected. 



Much wounding during tapping also aids in a similar way. 



SYMPTOMS OF ATTACK. 



A freshly exposed surface of Hevea attacked by Sphaeronema turns 

 darker in colour than normal in quite a short time (24 hours). In three 

 days the infected surface rots, and various species of saprophytic fungi 

 make their appearance on the dead tissue, the presence of these being 

 indicated by the tell-tale more or less complete cover of white mycelium. 

 This appearance is most noticeable one to two inches above the cut. 

 Portions of the tapped cortex sink in, forming depressed patches of 

 various sizes, which may in a bad case extend the whole length of the 

 cut. The affected portion frequently turns quite black. Later, in neg- 

 lected cases, the fungus penetrates the wood iV'-^", spreading vertically 

 up and down the wood fibres. 



The less serious cases where only small portions of the cortex become 

 depressed resemble Black Line Canker, but usually pycnidia may be 

 found, sometimes in considerable numbers. 



The damage caused by this disease when neglected is probably 

 greater than that due to any other bark disease of Hevea. The disease 

 continues as long as tapping is continued and is easily spread from tree 

 to tree by the knife. 



Cortex destroyed by Sphaeronema is frequented by small Diptera 



