CHAPTER XI 

 THE FUNCTIONS OF THE WOOD 



Two of the main functions of wood appear to be to transmit 

 water upwards from the roots to the branches and leaves, 

 and to furnish mechanical support. Of these, the latter 

 has been dealt with at length in the well-known researches 

 of Schwendener, which are summarized by Haberlandt in 

 his " Physiological Plant Anatomy/' and the former has 

 been discussed fully by Dixon in " Transpiration and the 

 Ascent of Sap." 



It must, however, be conceded that the wood has a 

 third function, one of nutrition in a narrow sense; for, to 

 be accurate, water is a nutritive substance. Accordingly, 

 it is with the transpiration stream considered as a medium 

 for the distribution of food materials that the author 

 proposes to deal in the present chapter. 



So long ago as 1858 Th. Hartig recognized that the 

 soluble products of the reserve materials found in the 

 wood parenchyma and the medullary rays must utilize the 

 tracheae as their channels of transport to the higher regions 

 of plants. This he demonstrated by the depletion of these 

 stores in ringed branches. He concluded that the materials 

 assimilated in the leaves are passed down in the bark and 

 stored in the wood parenchyma and medullary rays. In 

 spring these store materials are brought into solution, and 

 passed into the tracheae, where they rise with the upward 

 moving current of water from the roots. 



