106 Dr Wight on the Tree which produces 



The facts which I have detailed in this memoir seem to es- 

 tablish, 1st, that the extensive clearing of a country diminishes 

 the quantity of running water which flows over its surface; 2dly, 

 that it is impossible for us to determine, at present, whether 

 this diminution is owing to a smaller annual quantity of rain, 

 or to an increased evaporation of the surface-water, or to those 

 two causes combined ; 3dly, that the quantity of running water 

 does not appear to have varied in countries which have not been 

 subjected to any changes arising from the progress of cultiva- 

 tion; 4thly, that, independent of the preservation of surface 

 water, forests husband and regulate their flow ; 5thly, that 

 cultivation, when established in an arid country, which is not 

 covered with forests, dissipates a portion of its running streams ; 

 6thly, that, in clearings which are purely local, springs may 

 disappear, without there being any ground to conclude that the 

 annual quantity of rain has diminished ; and Tthly, that, draw- 

 ing our conclusions from the meteorological facts collected in 

 equinoxial regions, we may presume that the extensive clearing 

 of a country diminishes the annual quantity of rain which falls 

 upon it. 



On the Tree which produces the Gamboge of Commerce. 

 By Robert Wight, M. D. IVtth Reviarks, hj Dr 

 Graham. 



I AM induced to request a place in the Madras Journal, for the insertion 

 of a few remarks on the tree which produces the Gamboge of commerce, in 

 consequence of the following observations on it by Dr Graham, Professor of 

 Botany in Edinburgh, communicated by him in a letter dated 1 2th March 

 1836: " In consequence of having received specimens from Mrs Walker of 

 the tree which in Ceylon yields gamboge, I have been attending to the sub- 

 ject lately, and on Monday last, read some observations to the Royal Society 

 of Edinburgh about it. I have been obliged to dissent wholly from Arnott 

 and vou, that it is the Xanthochymus ovalifoUus, and Arnott now agrees with 

 me so far, but he has fallen into at least as great a blunder. It is undoubted- 

 ly, as I think, the Garcinia (Mangostana, Gcert.) Morella of Desrousseaux and 

 Gsertner. Arnott now thinks it Garcinia Zeylanica, which it cannot be, if 

 Roxburgh describes this with any degree of truth. In fact the Garcinia Aforella, 

 which I have said it is, is no Garcinia. Murray says the tree is the Stalagmitis 

 cambogioides, but his description will not apply to ray plant, from which I have 

 a great quantity of excellent gamboge. I have sent a specimen to Mr Don, 



