LIVING PARTS OF 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 conclusions can be drawn from this experiment as to the course 
followed by the sap ? 
From 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 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. 
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. Itscourse F'!¢. 55.—A Cutting Girdled and 
: sending down Roots from the 
is undoubtedly for the most part Upper Edge of the Girdled Ring. 
through the sieve-cells (Figs. 42— 
45), which are admirably adapted to convey liquids. In addi. 
tion to these general upward and downward movements of 
1 This may be made the subject of a protracted class-room experiment. Strong 
shoots of willow should be used for the purpose. 
