158 Ustuliiia Zonata [Lev.) Sacc. on Hevea Brasiliensis 



were obtained showing but live or six boreholes and the fungus working 

 actively in the wood, but no case was found where borers were entirely 

 absent. In the great majority of the trees, the association of insect and 

 fungus was very pronounced. The fungus was carefully isolated from 

 several of these trees and was identical with the cultures obtained from 

 specimen {A). 



Further supporting evidence for the connection between Ustulina 

 zonata and attacks by boring beetles was obtained in an experiment 

 described (9). In this experiment the bark of twenty-four rubber trees 

 was- scraped in order to see whether this treatment rendered them more 

 liable to insect and fungus attacks. The laticiferous system was not 

 injured in any way, the scraping being performed to compare heavy 

 scraping — the cork-cambium being removed — and light scraping — the 

 cork-cambium being left intact as far as possible. Five trees of the total 

 treated were quickly attacked, three by borers. Two of the three trees 

 attacked bv borers showed traces of Ustulina zonata in the bark five 

 weeks after the insects entered. In one tree, the fungus made beautiful 

 progress and daily observations were made. An interesting point is that 

 the borers disappeared after the first fortnight and the rate of growth of 

 the fungus in the wood of the stem and collar could be directly com- 

 pared. PI. IV, fig. 5 is a photograph taken four days after the trees were 

 scraped and shows the latex streaming down the trunk from the holes 

 made by the beetles. Fig. 6 shows the surface of the wood exposed with 

 the typical black lines formed by the fungus. PI. VIII, fig. 21 shows a 

 section through the diseased part six months after the scraping, and 

 a comparison with PI, VII, fig. 19, 'which represents a typical artificial 

 inoculation at the collar about six months old, shows that the rate of 

 growth of the fungus in the stem and collar is almost the same. 



This experiment (9) indicates that the important protective layer in 

 rubber trees is the outer layer of corky cells, and if this layer is injured, 

 they are liable to attack by boring beetles. The laticiferous layer affords 

 comparatively little protection against borer attacks beyond preventing 

 the entry of the first few insects. The first comers trying to enter were 

 trapped in the streaming latex, but later arrivals succeeded in entering 

 through places prepared by their j)redecessors. On the estates troubled 

 with leaf fires the scorching of the bark did not interfere with the pre- 

 sumed protective function of the laticiferous system of the trees, for the 

 latex streamed freely from the holes made by the borers. 



The above evidence affords a convincing explanation of the preva- 

 lence of borer attacks at the time of thinning out. When a tree is felled 



