6 PARA RUBBER. 



posed more or less longitudinally. In some cases the walls of the 

 cells are only incompletely disintegrated, and the flow of the latex 

 is, therefore, not as free as when the partition walls are completely 

 broken down. The disconnected series of cells in all stages of per- 

 foration is accountable for many of the variations in yield of 

 latex and rubber described elsewhere. 



Functions of the Latex. 



It is well-known that a system of milk tubes may or may not occur 

 in different species of plants, and that the presence of a latici- 

 ferous system is of importance in determining the identity of species. 

 Several natural orders, such as those which include species of 

 Euphorbia, Castilloa, Hevea, Funtumia, Landolphia, &c, are 

 characterized by large numbers of plants which possess milk tubes, 

 whereas other natural orders are not known to possess any laticiferous 

 species. It is also recognized that the number of species of plants, 

 possessing milk tubes, is greater in the tropics than in colder or more 

 temperate zones, and that many of the latex-bearing plants thrive on 

 rocky soils and in dry districts in the tropics. 



If one reflects on the thriving condition of widely different species 

 of latex-bearing plants in the temperate, sub-temperate, and tropi- 

 cal regions, and the behaviour of such plants under various conditions 

 the difficulty of ascribing a single function or series of functions 

 to the latex will be manifest. Each species must be considered 

 separately, and in the case of Hevea brasiliensis many observations 

 have been made and various theories propounded. 



Groom*, when dealing with this subject, pointed out that there 

 was no reason to beheve that the functions of the latex in all plants 

 are the same, or that one function should exclude the other. 



Function of Storing Water. 



The latex of Para rubber consists mainly of water and caoutchouc 

 globules together with small quantities of sugars, proteids, gums, 

 resins, mineral matter, &c. Most of the constituents cannot be re- 

 garded as forming reserve food, and even in the case of sugars and 

 proteids their presence in such small quantities would prevent their 

 being of vital importance to the plant in times of emergency. 

 Furthermore, the fact that the tubes arise, de novo, by a process of 

 perforation and decomposition, and during their ramifications in the 

 cortex are never in direct communication but contact only with the 

 vital elements of the bast, supports the contention that the small 

 quantities of food they contain are probably of very minor import- 

 ance to the plant. 



The water is, according to most observers, of more importance 

 than the other constituents. It is well-known that the flow of 

 latex is largely determined by the humidity of the air and the 

 quantity of water present in the soil. The increased flow which 

 follows the rain after a drought is often very remarkable. 



* Function of laticiferous tubes, Annals of Botany, 1889. 



