600 SCIENCE PROGRESS 



The percentage of water and caoutchouc will naturally vary 

 inversely. Para rubber is remarkable for the low proportion 

 of resin — a point much in its favour. Other rubbers usually 

 have more. The comparatively large amount of protein in the 

 latex is noteworthy ; a considerable part of it naturally becomes 

 incorporated with the rubber through coagulation. 



Lack of Strength in Rubber from Young Stems 



The possibility of preparing commercial rubber from the 

 young stems and leaves of caoutchouc-plants has often pre- 

 sented itself in the past; but in respect to Hevea and some 

 other rubber trees as well, there is one fatal objection to this 

 project. The latex from these parts of the plant produces 

 a "rubber" somewhat adhesive, with little elasticity and 

 strength. 1 



This is a peculiar point and has not yet been clearly 

 explained. The writer has suggested that perhaps the latex 

 formed in primary growth has a different composition from 

 that produced in the secondary tissues by the cambium. The 

 difference does not seem to be wholly due to a higher per- 

 centage of resin in the latex from the young organs, though 

 in some cases this may occur. A sticky weak caoutchouc may 

 show on analysis a chemical composition almost identical with 

 that of a standard product. 



The explanation evidently lies deeper, and may be bound 

 up in the mysteries surrounding " tackiness " in rubber, which 

 is receiving attention from Dr. Spence. 2 Plantation rubber 

 occasionally arrives ' on the market in a sticky state, though 

 despatched from the tropics in good condition. This change 

 and great deterioration have been laid to the charge of bacteria. 

 Spence shows reasons for thinking that the alteration is not 

 directly due to bacterial growth but rather to a change in 

 the physical nature of the rubber particles themselves, which 

 ordinary chemical analysis fails to reveal. There may be 

 some physical relationship between the weak adhesive caout- 

 chouc from young plant organs, the so-called " tacky " rubber 

 and that rendered permanently sticky by heat. 



Although the globules in the latex of rubber-yielding plants 



1 Parkin, Annals of Botany, 1900, 14, 203. 



8 Spence, India-Rubber Journal, Quart. Century No. 1909, 43. 



