110 



FOUNDATIONS OF BOTANY 



stood in water, as shown in Fig. 

 bell-jar, develop roots only at or 



76, and covered with a 

 near the upper edge of 

 the stripped portion, 1 

 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 



FIG. 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 



. .. FIG. 79. Unequal Growth of Kings 



Stem, that Side Of the Stem On O f Wood in nearly Horizontal 

 Which the manufacture of SUch Stem of a 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. 



