110 FOUNDATIONS OF BOTANY 
stood in water, as shown in Fig. 
76, and covered with a 
bell-jar, develop roots only at or near the upper edge of 
Fic. 78. — Diagrammatic Cross-Section of a 
Bundle from Sugar-Cane, showing Channels 
for Air and Water. (Magnified.) 
Air travels downward through the two large 
ducts d (and the two smaller ones between 
them). Water travels upward through the 
ducts and through the wood-cells in the 
region marked w. Water with dissolved 
plant-food travels downward through the 
sieve-cells in the region marked s. 
laterally through the stem, and 
these are at times of much im- 
portance to the plant. 
Since the liquid building mate- 
rial travels straight down the 
stem, that side of the stem on 
which the manufacture of such 
the stripped portion,! 
and this would seem to 
prove that such stems 
send their building ma- 
terial — the elaborated 
sap — largely at any rate 
down through the bark. 
Its course is undoubt- 
edly for the most part 
through the sieve-cells 
(Figs. 63, 64), which are 
admirably adapted to 
convey liquids. In ad- 
dition to these general 
upward and downward 
movements of sap, there 
must be local transfers 
Fia. 79. — Unequal Growth of Rings 
of Wood in nearly Horizontal 
Stem ofa Juniper. (Natural size.) 
material is going on most rapidly should grow fastest. 
1 This may be made the subject of a protracted class-room experiment. 
Strong shoots of willow should be used for the purpose. 
