104 



PLANT BIOLOGY 





ances, and the loss of weight will be noticed (Fig. 127). 98. Cu^l/ 

 a winter twig, seal the severed end with wax, and allow the twig 

 to lie several days ; it shrivels. There must be some upward 

 movement of water even in winter, else plants would shrivel 

 and die. 99. To illustrate sap pressure. 

 The upward movement of sap water often 

 takes place under considerable force. The 

 cause of this force, known as root pressure, 

 is not well understood. The pressure varies 

 with different plants and under different 

 conditions. To illustrate : 

 cut off a strong-growing 

 small plant near 

 the ground. By 

 means of a bit of 

 rubber tube attach 

 a glass tube with 

 a bore of approxi- 

 mately the diame- 

 ter of the stem. 

 Pour in a little 

 water. Observe 

 the rise of the 

 water due to the 

 pressure from be- 

 low (Fig. 128). Some plants yield a large 

 amount of water under a pressure sufficient 

 to raise a column several feet ; others force 

 out little, but under consider- 

 able pressure (less easily de- 

 monstrated). The vital pro- 

 cesses {i.e., the life processes). 

 100. The pupil 

 having studied 

 roots, stems, 

 and leaves, 

 should now 

 be able to de- 

 scribe the main 

 vital functions 

 of plants : what 

 is the root func- 

 tion? stem function? leaf function? 101. What 

 is meant by the "sap"? 102. Where and how 

 does the plant secure its water? oxygen? car- y li: r2g _]-<> show 

 bon? hydrogen? nitrogen? sulfur? potassium? sap Pressure. 



Fig. 126. — To illustrate 

 Transpiration. 



^ 



t ig. 127. — Loss of Water. 



