98 PARA RUBBER. 



Other trees, tapped at similar levels, show very large but 

 variable yields. 



Average Yielding Capacity of the Cortical Tissues. 



The yielding capacity of the Para rubber tree is influenced by 

 its constitution and environmental conditions, and it may, at first, 

 seem impossible to arrive at any reliable conclusions as to the rubber 

 capacity per square foot or yard of cortical tissue. Dr. Haas 

 has determined the rubber-yielding value, under known conditions, 

 per square metre of cortex for certain Para rubber trees in Java. A 

 large number of results will be required before anything definite can 

 be asserted, and the following figures should be useful for compari- 

 son with those of other observers. The experiments were carried 

 out at Henaratgoda between September 26, 1905, and February 13, 

 1906, on trees 15 to 20 years old. The original groove, about one- 

 quarter of an inch wide, was made without obtaining rubber in 

 quantity ; in subsequent operations the bark was removed by paring 

 only when the yield of latex obtained by pricking the tubes was 

 considered too small. The rubber was therefore obtained more by 

 incising rather than excising the latex tubes. 



The above results show what may, on an average, be expected 

 by different systems of tapping— spiral and herring-bone — from 

 parts of the tree from the base to a height of fifty feet. The trees, 

 on account of their age, had moderately thick bark tissues, and the 

 average yields per square foot are higher than those obtainable from 

 younger trees. It is important to note that an average yield of over 

 13 ounces of rubber may be obtained per square foot of excised 

 cortical tissue from the base up to 5 or 6 feet and from 6 to 16 

 feet from the base. It remains to be seen what proportion of 

 rubber the remaining and renewed bark will give. In a fairly 

 general way it may be stated that an increase in circumference 

 of five inches gives an increase in the basal tapping area of 360 

 square inches, and from such an area an average of about h lb. 

 of dry rubber may be extracted from the bark of trees younger 

 than those just dealt with. 



