64 PARA RUBBER. 



would follow. Parkin writes : * <: Personally I am not inclined to 

 look upon latex as playing an important part in nutrition, and 

 should imagine that if it were possible to extract all the latex 

 from such a tree as Hevea brasiliensis without greatly injuring 

 the other tissues, it would not be seriously harmed." 



It is, however, only reasonable to suppose that latex is of 

 some utility, if only a minor one, to the life of the plant, especi- 

 ally in view of the vast number of plants which contain it. As 

 the greater majority of these are either tropical or xerophilous 

 types, such as many Euphorbias, Asclepiads, and Dogbanes, it 

 is possible that one of the main functions of latex is to protect 

 the plant from too rapid transpiration. We are therefore led 

 to wonder whether, if Hevea were cultivated in a hot dry region 

 under irrigation, it would yield greater quantities of rubber than 

 in districts where more atmospheric moisture is obtained. Latex 

 is more abundant in Hevea trees when rains are plentiful, but 

 it is not so rich in caoutchouc as during dry weather. Latex 

 has certainly a beneficial effect in protecting the plant from 

 certain bark-eating insects. Longicorn bark-eating beetles have 

 been observed to attack the living bark of Heveas and immedi- 

 ately relinquish their efforts when the viscid latex commenced 

 to flow, although no other food was available. Were trees 

 drained of their latex they would obviously be more susceptible 

 to the depredations of such pests. 



Numerous instances are on record where the foliage-bearing 

 portions of Hevea trees have been broken off by wind, or 

 deliberately cut down so that nothing but the trunk remained, 

 and, although no foliage has been produced for several years, 

 they have yielded latex from which rubber of good physical 

 properties has been manufactured. 



CHEMICAL AND PHYSICAL PROPERTIES OF LATEX. 

 As far back as 1826 Faraday analysed the latex of Hevea 

 which was sent to Europe from Brazil, and found the following : 



Per Cent. 



Gum elastic - . 37.70 



Albuminous matter - - 1.90 



Bitter nitrogenous colouring principles - - 7.13 



Substances soluble in water - - - - 2 qo 



Wax - . .,, 



Water slightly acid - - 56.37 



* Circular, Royal Botanic Gardens, Ceylon, p. 114, June 1899. 



