83 



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 

 clean weeded estate especially on the slopes. 



Tn 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 of 

 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 the 

 excessive heating of the soil. More experiments are required t(^ 

 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 of 

 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 were 

 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 had 

 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 ymmg trees planted fariapart in clean- 

 weeded ground the loss of water from the upper layers of soil on a 



