The fallen leaves are kept on the ground in all estates to decay 
but a very large portion of the resulting humus must be swept away 
by the heavy storms of rain as there is nothing to prevent this in a 
dean weeded estate especially on the slopes. 
In sandy ground cleared and weeded in rubber estates I do not 
find the alga referred to above so that the wash here must be even 
worse than on the stiff clay soils where it protects the surface to some 
extent. 
ACTION OF SUNHEAT 
The action of the heat of the sun in cleared ground is another 
factor which has to be considered. It is not at all uncommon to see 
the ground beneath the rubber trees deeply cracked after hot weather. 
As Para Rubber roots high, and frequently the rootlets come very 
near the surface, under such circumstances a considerable number ot 
the small growing roots must be broken across by the cracking of the 
soil, and further the great heat on the exposed earth will probably 
injure the roots lying near the surface even if the soil in not cracked. 
Injuries caused by excessive heat, however, should only affect young 
trees, where the ground is insufficiently shaded by the trees them- 
selves A grass covering of the soil prevents cracking and also tie 
excessive heating of the soil. More experiments are required to 
decide how far sun heat on the bare soil is injurious to the young 
roots. It has been the custom in the Botanic Gardens to clear the 
soil round the palms of herbacious plants, grass, and other weeds, 
leaving a circle of bare soil round each plant. This was done for 
convenience in manuring. On one occasion however, the ground 
round the palms was turfed up to the stem with the result that they 
made quite a surprising growth, now the greater part of the roots ot 
the palms were really under the grass, and the only ones affected 
were those close to the base of the trees. The only conceivable cause 
of improvement from turfing up the circles is that these roots weu 
protected from sunheat, and consequent excessive drying. Palms do 
not give much shade with their leaves, and the roots close to the 
stem are practically exposed to the full sun all day. 
Another little observation illustrating the action of the sun in 
drying exposed soil, is this. Walking along the main road in the 
late afteroon I noticed that the road was marked by darker lines cor- 
responding to the shadows of the roadside trees from the south-west. 
The trunks of the branches being marked out on the road. It had 
been somewhat cloudy most of the day and the sun was not then 
shining. On examining the dark shadowy patches I found that they 
were due to the greater dampness of the ground where the trees hac 
protected it from the full rays of the afternoon sun which had thor- 
oughly dried the rest of the road. There had been no rain during 
the day, and the dampness was probably caused by the dew of the 
previous night. In the case of young trees planted far, apart in clean- 
weeded ground the loss of water from the upper layers of soil on a 
