F. T. Brooks -2)7 



Pure cultures of fche fungus arc easily established by sowing 

 conidia upon sterilised Mocks of Herat wood or upon potato agar. 

 A white mycelium rapidly develops which assumes first a pink and then 

 a brownish tinge. Alter a time, sessile aggregations of spores of a 

 yellowish pink colour arise on both media and these are often arranged 

 in concentric zones. These spores are hyaline, oval, and very variable 

 in size, the average limits being 16-20jii x 6-8/m though some are much 

 smaller (cf. Plate XXXIV, fig. 4). 



Spherical, thick-walled resting spores 9-10/u, in diameter are formed 

 in the hyphae and at the ends of short branches ; these spores are brown 

 in colour when mature. On blocks of Hevea wood, stalked conidia] 

 fructifications often arise similar to those which occur naturally. The 

 mycelium penetrates the middle of these wood blocks, being specially 

 abundant in the vessels and medullary rays. There was no sign of 

 the formation of perithecia in these cultures. 



Roots of seedling rubber plants in pots and of 4 year old trees 

 on hilly land were inoculated with pure culture material of the fungus. 

 In some cases the roots were wounded, in others the wood block bearing 

 the mycelium, or the culture on agar, was placed against uninjured 

 tissues. After an interval of nearly five months none of these plants 

 (16 in all) showed signs of infection. This negative result points to 

 the possibility that some, at present unknown, condition which disposes 

 to susceptibility must exist before the fungus can invade the roots 

 of a rubber tree. As pointed out above, bad aeration of the soil con- 

 sequent on deficient drainage may be a factor in inducing the requisite 

 condition for the fungus to enter. 



Rubber trees affected by this fungus should be cut out and burnt. 

 The attack is usually far advanced before the tree is seen to be diseased, 

 hence it is generally not worth while to try to save the tree by excision 

 of the affected parts. There is yet no evidence that the fungus spreads 

 by subterranean strands but neighbouring trees should be examined, 

 and to be on the safe side a trench should be dug around the affected 

 tree at such a distance as to preclude the possibility of underground 

 infection. If it is intended to replant the affected area after an interval, 

 the soil should be deeply dug, all timber removed, and a liberal dressing 

 of lime applied. This disease spreads more slowly than Forms lignosus, 

 and though it is not abundant in Malaya it is probable that the loss 

 of some old rubber trees attributed to Fames was really caused by 

 Sphaerostilbe repens. 



