82 
DENUDATION. 
The rainfall in the Malay Peninsula is very heavy, and in 
exposed situations and on slopes the loss of soil in a heavy shower is 
very large as has been already stated. Where the rain runs over 
these slopes, in a very few minutes it is seen to be quite opaque from 
the soil washed off. With this soil goes all exposed humus, decayed 
leaves and sticks. The rain, however, does not run off equally over 
the ground, it soon runs in channels formed first by some inequali- 
ties in the ground and then by deepening these. Between these the 
ground of the ordinary yellow clay, become covered with a thin crust 
of an alga. In dry open spots in the Botanic Gardens, I find this 
to be of a dark red colour, and it appears to be gelatinous alga allied 
to A ostfc. In damp shady spots the alga is green. 
There are probably several species which form these thin crusts, 
i hese prevent denudation to a large extent, the water simplv running 
over the alga, and not touching the soil. If left, mosses and hepatics 
grow over the alga and eventually higher forms of plants. Should 
the water rush be too strong in any part of the ground, denudation 
takes place at a very rapid rate. When grass grows over the *tiff clay 
soil it prevents denudation to a very much larger extent, and in a 
lew years produces a layer of humus which fact itself shows that 
denudation has been stopped, the roots also break up the stiff clay 
soil for some depth, and render it possible for other roots to penetrate. 
In examining, the rubber plantations in the Botanic Garden a 
very strong contrast is to be noticed where a path through the trees has 
been opened and kept free of grass. The ground is covered with roots 
o Para rubber trees, the tops of which are an inch and a half or more 
above the soil. Examining the ground on the other side of the tree, 
which is not weeded I find the corresponding roots as much or more 
below ground, so that the opened path (not opened many years, and 
well shaded so that the rainfall is broken up by the foliage above and 
does not fall so heavily on the ground) has lost four or five inches of 
sou since it was opened. 
In the case of anothor lot of trees seen in Perak, where the 
ground was bare, sloping and of stiff clay, roots as thick as the wrist 
were completely exposed and dead, the ends being gone. These 
roots must have been originally some distance under ground. The 
loots o the Para rubber lie usually very high, but this doubtless 
depends to a large extent on the depth of the water, in the soil. In 
t le damper parts of the Botanic Gardens the rootlets of the Para 
ru i er come quite to tbe surface wherever there are any decayed 
leaves and even sometimes rise up between scraps of detached bark 
on t e, trunk of the tree itself. Dead wood, old stumps are quickly 
invested and permeated by them. This I think shows that Para 
^iinbei demands good humus and is ready to utilize all it can find. 
