104 



BEGLVNERS' BOTANY 



Fig 



ances, and the loss of weight will be noticed (Fig. 127). 98. Cut 

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

 to he 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 Hj-^J 



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 httle, but under consider- \ 



able pressure (less easily de- 

 monstrated). The vital pro- 

 'f^^-^^""''^^ 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- 

 bon? hydrogen? nitrogen? sulfur? potassium? 



126. — To ILLUSTRATE 



Transpiration. 



Loss OF Water. 



Fig. 128. — To SHOW 

 Sap Pressure. 



