74 



EXPERIMENTS WITH PLANTS 



the plant can compress the spring no further, remove 

 it, invert the bottles, substitute for the inner bottle a 

 larger one of the same diameter, and pour shot into it 



until the spring is compres- 

 sed to the same point as it 

 was by the plant. The weight 

 of this bottle with the con- 

 tained shot, plus the weight 

 of the inner bottle and cotton 

 (since the plant raised these" 

 in addition to compressing 

 the spring) , will give the pres- 

 sure exerted by the plant: if 

 we divide this by the area of 

 the cross -section of the stem 

 just back of the crook we 

 shall obtain the number of 

 pounds pressure to the square 

 inch. Thus, in one case the 



BO. Modification of the apparatus P lant exerted a pressure of 

 shown in Fig. 59. one poun( j. The diameter of 



the stem just back of the crook was one -eighth inch. 

 The equation is 



1 pound =1 



3.1416 x 



m ' 



It is interesting to note, in this connection, that 

 the pressure of steam in the boilers of ordinary sta- 



