RUBBER PLANTING 199 



period of waiting for satisfactory crops is consequently 

 a long one. 



The Castilloa has generally been closely planted. 

 From 200 to 300 trees per acre is by no means an un- 

 common estimate. Since the growth of Castilloa in the 

 rich soils of Mexico appears to be considerably more 

 rapid than the average recorded for Hevea on plantations* 

 there can be little doubt that the trees are greatly 

 crowded. 



The trees are only tapped at intervals of about four 

 months. The method employed is purely one of incision, 

 and consists in cutting a few slanting or V-shaped 

 channels in the bark. The rubber is usually prepared 

 from the latex by a process of creaming. In this pro- 

 cess the latex is diluted with a considerable bulk of 

 water and, after stirring, is allowed to stand in tanks 

 until the whole of the rubber has collected as a cream 

 upon the surface. The clear liquid is then drawn off 

 from below, and the whole process is repeated until dirt 

 and soluble impurities have largely been removed. The 

 rubber is then finally dried and rolled into sheets. 

 Centrifugal machines are also sometimes employed. In 

 this way much time can be saved, and the washing is 

 more completely carried out. 



In Ceylon very fine samples of smoked sheet rubber 

 have been prepared from Castilloa latex. The cultiva- 

 tion, never very extensive, has however been almost 

 entirely given up in favour of Hevea. In the West 

 Indies Castilloa is still under trial, but only on a small 



