XI 



ABSORPTION AND MOVEMENT OF WATER 



How the Water Travels from the Roots to the 

 Leaves. The water which, as we have seen, is forced into 

 the xylem vessels of the root finds its way to the leaves (as far as 

 we know at present) up the interior of the vessels of the 

 stem. Professor Dixon, and Dr. Joly, found that if they 

 blocked up the interior of the vessels with paraffin-wax, only a 

 little water found its way up the stem, and the leaves on the 

 branch soon flagged. It would take far too long for the large 

 quantity of water which the plant requires to pass either up the 

 parenchyma cells, or through the cell walls. The water is able 

 to move faster up the interior of the vessels than in any other 

 direction. 



The Transpiration Current. The current of water 

 which passes up the stem from the roots to the leaves, to make 

 good that lost by transpiration, is called the transpiration 



FIG. 161. Diagram illustrating how the water moves up a stem, i, A normal 

 branch from the Oak in water, the leaves of which are fresh ; 2, a branch of the 

 Oak with the tissues removed down to the new wood ; 3, a similar branch with 

 the new wood taken out, the leaves are dried up ; 4, 5, sections of the same. 



current. This current travels up the stem of a woody plant, 

 but only through the outer and younger rings (p. 107). The 

 heart wood of an old tree never takes part in the conduction of 

 water, but only the newer rings of the sap wood. The reason 

 why the transpiration current ascends as it does in some trees 

 to a height of over a hundred feet is not fully understood, and 



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