THE ROOTS OF THE HEVEA 35 



be accounted for, it being clear that the root-pressure and the 

 evaporation through the stomata cannot be powerful enough 

 to propel the water the whole distance. Unfortunately, how 

 the water is enabled to travel this distance is not yet decided, 

 for of the various hypotheses advanced none receive general 

 acceptance. 



The whole complicated process of water-supply and dis- 

 charge is admirably conceived, and is carried out by these 

 minute living-cell engineers working together in perfect 

 harmony, as if each cell seemed to understand very well not 

 only its own duty but that it was being backed up by its 

 neighbour's activities. 



