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 zoogloea form of Crenothrix with 

 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. Lndeed 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 moluccanm 

 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 tw T elve 

 feet. The root where it started to ascend the palm, was about li 

 inches through. The oil palm was at one time covered with ferns 

 Tkamnopteris and Polypodium, growing on the soil held by the leaf bases 

 on the trunk. 



Albizzia is a very strong rooter sending its roots to a long distance, 

 but I think it is unusual to rind so large a root of a tree climbing 

 spirally upwards. 



Ascending roots occur in Mangroves, Bhizophora etc., and in 

 Grdmmatophylhim, 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, 



