PARA-RUBBER CULTIVATION 411 



East Africa, has failed to get it to respond to multiple 

 tapping. 



The Function of Latex. — A few words on the question of the 

 function of latex are called for here. It is still largely a problem 

 awaiting solution. 



A nutritive function for the laticiferous tubes was at one 

 time upheld. They were supposed to act as conductors of 

 plastic material, especially of proteins, and were considered in 

 some cases partly to replace the sieve tubes. Adherence to 

 such a view has lost ground in recent years. 



Spence, 1 however, has recently revived the nutritive view on 

 somewhat startling lines. His studies on the oxidising enzymes 

 of latex has led him to regard the caoutchouc as a food reserve, 

 which by means of these ferments may be oxidised and broken 

 down into simple carbohydrates for the plant's use. Physio- 

 logists will require much evidence before accepting such a 

 novel theory. 



That the tubes conduct or store food materials for the plant 

 seems doubtful. Primarily the latex may be regarded rather as 

 a waste product, and the tubes containing it as genetically related 

 to, and a further development of, secretory sacs. But the substi- 

 tution of an extensive system of communicating tubes in place 

 of isolated sacs apparently implies the adoption of some new 

 function, in addition to that of removing the waste products of 

 metabolism. A conducting function is the one which suggests 

 itself. The tubes may form channels for the conveyance 

 and storage of water. Laticiferous plants, at any rate the 

 arborescent ones, are distinctly numerous in the tropics, where 

 transpiration at times is excessive, especially during the dry 

 season. 



Again, the theory has been advanced that the latex serves 

 as a protection against insects and fungi. In respect to an 

 insect, a puncture or bite will result in an outflow of latex, 

 which may interfere with its further operations or prove dis- 

 tasteful to it. The penetration of a fungus through a wound 

 may be prevented by the latex which oozes out, forming an 

 impenetrable layer. This supposed protective function for 

 latex must be investigated separately for each species in its 

 original surroundings. The laticiferous system may have 

 been evolved to repel certain foes occurring in the natural 



1 D. Spence, Bio-Chemical Journal, 1908, iii. 179-81. 



