MOVEMENT OF LIQUIDS IX THE STEM 



75 



From the familiar facts that ordinary forest trees apparently 

 flourish as well after the almost complete decay and removal of 

 their heartwood, and that many kinds will live and grow for a 

 considerable time after a ring of bark extending all round the 

 trunk has been removed, it may readily be inferred that the 

 crude sap in trees must rise through some portion of the newer 

 layers of the wood. A tree girdled by the removal of a ring of 



FIG. 74. A cutting girdled and 

 sending down roots from the 

 upper edge of the girdled 



FIG. 75. Diagrammatic cross section of a 

 bundle from sugar cane, showing chan- 

 nels for water and dissolved plant food 



Water travels upward through the vessels d 

 and through the wood cells in the region 

 marked w. Water with dissolved plant 

 food travels downward through the sieve 



ring 



tubes in the region s. 



Magnified 



sapwood promptly dies. After the removal of a ring of bark a 

 tree dies from starvation of the roots (Sec. 88 ; also see Fig. 394). 

 88. Downward movement of liquids. Most dicotyledonous 

 stems, when stripped of a ring of bark and then set in water, 

 as shown in Fig. 74, and covered with a bell jar, develop roots 

 only at or near the upper edge of the stripped portion. This 

 would seem to prove that such stems send their building mate- 

 rial - - the elaborated sap - - largely, at any rate, down through 



