LIVING PARTS OF THE STEM 



109 



Examine longitudinal sections o^ some of the twigs, the potatoes, 

 and the roots. In drawing conclusions about the channels through 

 which the ink has risen (those through which the newly absorbed 

 soil-water most readily trav- 

 els), bear in mind the fact 

 that a slow soakage of the 

 red ink will take place in 

 all directions, and therefore 

 pay attention only to the 

 strongly colored spots or 

 lines. 



What conclusions can be 

 drawn from this experiment 

 as to the course followed by 

 the sap? 



From the familiar 

 facts that ordinary for- 

 est 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 consider- 

 able time after a ring of 

 bark extending all round 

 the trunk has been re- 

 moved, 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 sapwood promptly dies. 



118. Downward Movement of Liquids. Most dicoty- 

 ledonous stems, when stripped of a ring of bark and then 



FIG. 77. Channels for the Movement of 

 Water, upward and downward. 



The heavy black lines in roots, stems, and 

 leaves show the course of the fibro-vascular 

 bundles through which the principal move- 

 ments of water take place. 



