137 
fact seem to form small water conduits, and the current of water 
apparently enlarges them to some extent. The water adopts these 
passages before the roots are quite decayed, and probably also during 
life. These passages are lined with a coating of ferruginous slime and 
I have had an opportunity of examining some of this taken from a 
depth of about two feet in the Botanic Gardens. The slimy ferrugi- 
neous lining is composed of the zoogioea form of Crenothrix mth 
abundance of the free swimming spores as well, simple and dividing. 
This plant seems only to occur on the old root passages and on the 
roots themselves less abundantly, I do not see it however on living 
roots. Indeed the clay and root are so closely in apposition that there 
is but little room for its growth. The development of this iron- 
depositing Alga in the water channels through the clay is certainly to a 
large extent the origin of our laterite. The alga does not apparently 
require light for its growth at least in the bacterial form, as it is in 
these cases quite subterranean. At what depth it can live I have no 
means of knowing at present. This would probably depend on the 
waterflow. In light or sandy soils the root tubes would probably fall 
in when the roots decayed away, and not serving as water- passages 
the alga would not be able to grow there, so that in such soils one does 
not get the iron oxide deposit. In the case of springs permeating the 
stiff clay soils, and producing at their mouths a large growth of Cre- 
nothrix as is the case near the garden lake as described in a previous 
paper, no cleaning of the pond or pool at their mouth would prevent 
this as the plant is growing at considerable depth in the soil through 
which the spring flows. 
H. N. Ridley. 
CURIOUS ROOT-DEVELOPMENT OF ALBIZZIA. 
In the Singapore Botanic Gardens a tree of Aleurites moluccatius 
was growing in an open spot, and from one side emitted a stout root 
lying close to the surface of the soil. This root after going in a 
northern direction curved east and grew towards an oil palm at a 
distance of about 20 feet. On arriving at the palm it ascended in 
a spiral round the trunk till it reached the top, a height of about twelve 
feet. The root where it started to ascend the palm, was about 1^ 
inches through. The oil palm was at one time covered with ferns 
Thamnopteris and Polypodium, growing on the soil held by the leaf bases 
on the trunk. 
Albizzia is a very strong rooter sending its roots to along distance, 
but I think it is unusual to find so large a root of a tree climbing 
spirally upwards. 
Ascending roots occur in Mangroves, Bhizophora etc., and in 
Grdmmatophylhm, but these are short and specially modified rootlets 
used in aerating the plant, and the para rubber often sends rootlets 
upwards on old stumps or pieces of wood, or even beneath partially 
detached fragments of its own bark, but I do not ever remember to have 
seen such an exceptional development of ascending roots in any tree 
as in this Albizzia. 
H. N. Ridley. 
