io8 



TRANSPORT OF WATER AND SOIL SOLUTES 



But in one noteworthy detail they are very unlike wood fibers, 

 namely, their walls have numerous and large bordered pits, and 

 it is this that fits them for water highways (Fig. 51). 



The bordered pit is a thin area in the wall with an overhang- 

 ing border. The thin place is clearly to facilitate the passage 

 of water and solutes, and the border serves the double purpose 



FIG. 52. Diagrammatic representation of a block of pine wood highly magnified, a, 

 Early growth; b, late growth; c, intercellular space; d, bordered pit in tangential wall of late 

 growth; TO, /and e, bordered pit in radial wall of early growth from different points of view; 

 h, row of medullary cells for carrying food ; g, row of medullary ray cells for carrying water; 

 k, thin place in radial wall of ray cells that carry food. 



