52 RUBBER AND 



the expense of valuable food material, containing as it 

 does large quantities of carbon as well as a considerable 

 percentage of proteid material. There seems to be 

 no reason for doubting that the removal of latex causes 

 a sensible drain upon the supply of food available for 

 general growth. 



It has been suggested that latex vessels serve as 

 additional channels for the transport of food; and it 

 has been stated that the phloem is poorly developed in 

 laticiferous plants. This is not the case in the prin- 

 cipal kinds of rubber trees grown upon plantations, all 

 of which possess a highly developed system of sieve 

 tubes. Other functions which have been attributed to 

 the latex vessels are storage of food, storage of water, 

 storage of excretory products, or a combination of 

 any two or more of the functions already named; or 

 finally protection against the attacks of insects and 

 other enemies. None of these suggestions, except the 

 last, appear to be based on any satisfactory evidence, 

 On the other hand, latex undoubtedly serves a pro- 

 tective function. Any area of bark which has been 

 entirely depleted of latex, owing to disease or other 

 causes, is usually soon riddled by boring insects. These 

 seldom or never attack bark in which a good supply of 

 latex is present. Whether this function can be regarded 

 as a sufficient cause to account for the separate evolu- 

 tion of such an elaborate system in several different 

 branches of the vegetable kingdom, is a question which 

 we may leave for the discussion of theorists. 



