aR 
crowding. This results in a diminished amount of light and 
air, 1.e., free ventilation, reaching ihe trees. his factor does 
not influence the spread of root-rot on old trees to an appreciable 
extent and if bark renewal is not interfered with, losses owing to 
root disease can be compensated for. 
If free ventilation becomes necessary in the plantations this 
satisfactory method of allowing for diseased trees cannot be 
lowed. Investigations in rubber-growing countries other than 
Malaya show that free access of light and air is one of the 
essential conditions in combating Bark diseases of Hevea 
brasiliensis. Bark diseases were practically unknown in Malaya 
up to 1916 and as long as serious bark affections were not 
reported the position could be considered satisfactory. 
The previous article gives a short account of the serious out- 
breaks of Bark disease observed in Malaya in 1916. Treatment 
necessitates a vigorous thinning-out to the minimum number of 
trees per acre commensurate with profitable working. This 
number might be termed the ‘‘ working number,” for con- 
venience 
Conditions for the spread of fungus diseases are probably more 
favorable in Malaya than in any other rubber-growing countries. 
The atmospheric humidity is always high; there is no pro- 
nounced dry season when disease-producing fungi lie dormant 
which enables planters in Ceylon and Java to control diseases, 
especially those of the bark, more easily. The plantations 
are opened from virgin jungle, and as a consequence 
there are large numbers of jungle stumps and logs left in the 
ground to encourage disease. e troublesome root-rots in 
Malaya all originate from rotting jungle timber and stumps. 
Thus countries like Ceylon and Java, where large acreages of 
rubber are grown on land which has been cultivated for several 
hundred years, have a considerable advantage, for the original 
jungle stumps and timber liave long ago disappeared, and there 
is little chance of the root-rots appearing unless previous crops 
were attacked by the same fungi. Fungus diseases again are 
always most dangerous where there are large acreages under 
one crop, for no obstacles to the passage of spores exist unless 
jungle belts are interposed between the cultivated areas. In 
Malaya the whole of the peninsula is under rubber, and though 
jungle belts are provided they are not wide enough to be effective 
In preventing the spread of fungus diseases. Pink disease is a 
case in point; the fungus causing Pink disease reported from 
three small centres in 1912 had spread practically over the whole 
peninsula by 1914. : 
These facts are brought forward to support the view that 
there is every chance of Bark diseases spreading and becoming 
general throughout Malaya, and to indicate that the experiences 
of Malayan planters are likely to be different from those of Cev- 
lon and Java. Experience obtained in the latter countries 
Cannot be quoted as necessarily applying to Malaya. 
Until the discovery of bark diseases Malayan plantations could 
compensate for disease losses by keeping more than the ‘‘ work- 
ing number”’ of trees ner acre. This position is now untenable 
