28 PLANT PHYSIOLOGY 



altitudes. This, coupled with the fact that soil organisms give off 

 large quantities of carbon dioxide, may produce a layer next the 

 soil especially rich in carbon dioxide, which may be exceptionally 

 favorable for plants near the ground. 



j The Regulatory Action of Water. — Since carbon dioxide is 

 soluble in water, there exists an equilibrium between the carbon 

 dioxide dissolved in the oceans, streams, and lakes and that present 

 in the air above these bodies of water. Water generally contains 

 a bit more carbon dioxide than the air above it, and, as the amount 

 above increases, still more dissolves in the water and becomes 

 combined in the form of carbonates with the ocean salts. If 

 the air above diminishes below normal in the amount of carbon 

 dioxide contained, the ocean gives up some of that dissolved and 

 combined in it, thus serving as an autoregulator of the amount 

 present in the air. 



The Carbon Dioxide in the Coal Age. — In Carboniferous times 

 (250 to 500 million years ago) when the coal was formed, there was 

 evidently more carbon dioxide present in the air than now. The 

 warmer temperature of the earth and seas would not permit so 

 much to be dissolved in the oceans as at present, and there seems 

 to have been a great excess in the air. This permitted the luxuri- 

 ant growth of vegetation which covered the now temperate regions 

 of the earth at that distant period. The excess of production over 

 consumption and decay of that age, we are burning at the present 

 time. The carbon molecules which were removed from the Car- 

 boniferous carbon dioxide by the Paleozoic chlorophyll are once 

 more permitted to combine with oxygen and go back to the in- 

 organic state from which they came so long ago. 



QUESTIONS AND PROBLEMS 



1. What was Wohler's contribution to chemistry? 



2. If a bushel of potatoes contains 35 lbs. of starch, how much of this is 

 carbon? 



3. How do plants and animals differ in their use of carbohydrates? Of 

 what advantage is this to animals? 



4. Many elementary texts state that plants differ from animals in that 

 they (plants) use inorganic foods. Criticize this statement. 



5. Explain the results of the demonstration experiments described on 

 page 25. 



6. Why is photosynthesis "the most fundamental fact in science"? 



7. A good crop of corn is 75 bushels to the acre. If one-th3rd of this is 



