22 



must then lie fallow from exhaustion for years. Furthermore, it 

 is the duty of scientific research, based on well-established facts, to 

 lend a helping hand, when the experience of practical men is at 

 variance. 



These were the ideas that guided me in my experiments. I 

 had to begin with an investigation of the influence exercised by 

 ordinary girdling on the transport of sap in the stem of Hevea, 

 and in connection with this, I had to compare the changes in 

 the distribution of sap in the stem after the tree had been tapped 

 in accordance with the various tapping systems in vogue. For 

 my purpose it was sufficient to ascertain the distribution of starch, 

 formed from organic material assimilated in the leaves and 

 transported in the form of reducing sugar 6 through the channels 

 of the stem, and which chiefly fills the stem reservoirs. It requires 

 very little trouble to prove its existence. It is well-known that 

 the so-called iodine test is sufficient. When treated with a 

 solution of iodine in diluted alcohol the starch-grains rapidly turn 

 blue. If during these experiments, the starch has disappeared 

 from tissues, in which its existence had been already proved, there 

 are two alternatives, either it has become soluble and in this, 

 condition has remained in the tissues, or it has been conveyed 

 where it was required and has been utilized. If starch has been 

 dissolved, it is easy to prove the product of solution, reducing 

 sugar, by a treatment with Fehling's Solution. Other substances 

 besides starch and reducing sugar were not taken into considera- 

 tion at the investigation. (Whether it is desirable, or not, to. 

 include other substances, such as albumen and ammides, in our 

 research for the purpose of determining the value of the various, 

 tapping systems, time alone will enable us to decide. 



b Reduzierende Zitcker must be translated " reducing sugar." It 

 is a more comprehensive term than glucose. It includes glucose, cevulose. 

 grape sugar, and fruit sugar, but not cane sugar -in fact any sugar that 

 reduces Fehling's solution. Tr. 



