LIVING PAETS OP THE STEM. 



69 



through which the ink has traveled. Repeat with several potatoes, cut 

 crosswise through the middle. For the sake of comparison between roots 

 and stems, treat any convenient root, such as a parsnip, in the same way. 



Examine longitudinal sections of some of the twigs, the potatoes, and 

 the roots. In drawing conclusions about the channels through which the 

 ink has risen (which are those through which the crude sap most readily 

 travels), 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 concliisions can be drawn from this experiment as to the course 

 followed by the sap ? 



Trom the familiar facts that ordinary forest trees appar- 

 ently 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 extend- 

 ing all round t^he trunk has been removed, it may readily be 

 inferred that tl;ie crude sap in trees 

 must rise through some portion of 

 the newer layers of the wood. 



Most dicotyledonous stems, 

 when stripped of a ring of bark 

 and then stood in water, as shown 

 in Fig. 55, develop roots only at 

 or near the upper edge of the 

 stripped portion,^ and this would 

 seem to prove that such stems send 

 their building-material — the elab- 

 orated sap — largely at any rate 

 down through the bark. Its course 

 is undoubtedly for the most part 

 through the sieve-cells (Mgs. 42- 



45), which are admirably adapted to convey liquids. In addi. 

 tion to these general upward and downward movements of 



Pie. 55.— A Cutting Girdled and 

 sending down Boots from the 

 Upper Edge of the Girdled King. 



1 This may be made the subject of a protracted class-room experiment. Strong 

 shoots of willow should be used for the purpose. 



