44 PLANT PHYSIOLOGY 



trace of carbon-compounds, thrive perfectly. 3. Green 

 plants cultivated in water holding in solution the ordinary 

 soil constituents except the carbon compounds, also thrive 

 perfectly. 4. Submersed water plants cultivated in water 

 containing all the usual salts, but no trace of carbon-diox- 

 ide, soon cease to grow and presently die. The second and 

 third of these experiments demonstrate the error in the old 

 theory and in the present popular belief that leaf-mould, 

 loam, manures, and fertilizers, natural and artificial, are 

 valuable because of their carbon content. Besides the 

 phosphates which they contain, it is probable that the only 

 valuable constituents are the nitrates. 



Carbon-dioxide forms about five-hundredths of one per 

 cent, of normally pure air (.05%). From this we can calcu- 

 late the percentage of carbon thus : 



Atomic weight of carbon = 12 C = 12 

 " oxygen = 16 0, = 32 

 CO, = 44 

 C 12 _ 3 

 CO, ~ 44 ~ 11 

 CO, = .05% of air. 



C =.05 ^ Jx=-0135+ 

 .-. C =.01% of air. 



From figures given by Noll* we can calculate the volume of 

 air necessary to furnish the carbon contained in a tree 

 weighing 11,000 pounds dry and 50% of the dry weight of 

 which (5,500 lbs. =2,500 Kilos) is carbon. Thus: 

 10,000 litres of air contain 5 litres of CO, 

 5 " " CO, weigh 10 gr. 

 of this C weighs ^ = 2 gr. 

 .•. 5,000 litres of air contain 1 gr. of C. 

 2,500 Kilos = 2,500,000 grs. 

 .-. 2,500,000 X 5,000 = 12,500,000,000 litres 



= 12,500,000 cubic metres 

 = 16,125,000 " yards 

 Hence 16,125,000 cubic yards of air must have their car- 



* Text-book of Botany, by Strasburger, Noll, Schenck, Schimper, trans- 

 lated by Porter, p. 196. New York, 1898. 



