THE ORIGIN OF ORGANIC MATTER 37 



In view of the fact that the amount of oxygen required for photo- 

 synthetic activity is relatively very small we can confine our attention to 

 the carbon dioxide. The calculated difference in the percentage distribu- 

 tion of gases in the atmosphere with increasing altitude -'' are also of no 

 immediate significance to our subject, as we must naturally confine our 

 attention to land areas capable of supporting vegetative growth. 



There is still some debate regarding the exact value of the carbon 

 dioxide content of the atmosphere, more i>articularly the constancy of the 

 amount present with change in location and weather conditions. It should 

 be stated immediately that it is highly probable that many of the dis- 

 cordant results unquestionably are due to the fact that different methods 

 of analysis were used and, simple as the problem may seem, thoroughly 

 reliable methods of air analysis have been worked out only relatively re- 

 cently. The tension of the water vapor in the atmosphere may cause a 

 considerable variation and some of the analyses have apparently been cor- 

 rected for moisture while others have not. Moreover, the place of taking 

 the sample whether this is, for instance, close to the ground or not may 

 be of considerable influence. Sources of carbon dioxide even when these 

 are some distance away may influence results. Thus Reiset -^ took samples 

 8 kilometers from the city of Dieppe and found a mean value of 0.02917 

 volume per cent COo. The proximity of a drove of sheep raised this 

 value to 0.03178. 



Benedict ^^ reports remarkably constant values for carbon dioxide and 

 oxygen. He concludes : "The results of analyses of air taken near the 

 laboratory showed no material fluctuations in oxygen percentage during 

 a period extending from April 15, 1911, to January 30, 1912. This con- 

 stancy was maintained in spite of all possible alteration in weather condi- 

 tions, changes in barometer, thermometer, humidity, and wind direction 

 and strength; furthermore, the experiments were made before, during, 

 and after the vegetative season. The average result of 212 analyses showed 

 0.031 per cent of carbon dioxide and 20.938 per cent of oxygen. The 

 analyses of air collected over the ocean, at two dift'erent times of the year, 

 and on top of Pike's Peak, gave essentially similar results." The carbon 

 dioxide-content in crowded city streets was found to be slightly higher 

 than normal, while samples taken in New York and Boston subway 

 stations contained about twice the normal amount. 



Among the older analyses reported one finds very considerable varia- 

 tions in the amount of CO2. By some writers much importance has been 

 attached to these variations. In fact Reinau ^=* has developed an elaborate 

 theory on the basis of these observations, in which he stresses the signifi- 

 cance of periodic variations in carbon dioxide content of the atmosphere. 



'"Humphreys, F. J., Physics of the Air. Philadelphia, 1920, p. 60. 



^Reiset, J. A., Compt. rend., 88, 1007 (1879). c^ . ^ r 



'■" Benedict, F. G., The Composition of the Atmosphere with Special Reference 

 to its Oxygen Content. Carnegie Inst, of Washington. Pub. No. 166 (1912), 

 p. 114. 



"'Reinau, E., Kohlensaure und Pflanzen. Halle, 1920. 



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