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,^ 

 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 



Fig. 78. — niagrammatio Cross-Section of a COUVey liqUlds. In ad- 

 Bundle from Sugar-Cane, showing Channels (Jj^ion tO thcSC general 

 for Air and Water. (Magnified.) ° 



V *v . 1 upward and downward 



Air travels downward through the two large J^ 

 ducts d (and the two smaller ones between mOVCmentS of Sap, there 

 them). Water travels upward through the , , , transfprs 



ducts and through the wood-cells in the mUSt DC iOCai tranSICrS 

 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 



■J £ i. 1. riQ.79.— Unequal Srowthof Rings 



stem, that side OI the stem on of 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. 



