120 LECTURE VII. 



general results are that when the proportion of oxygen present 

 is large, that of carbon dioxide is small, and vic$ versa, the 

 proportion of carbon dioxide being smallest in the winter. 

 In most cases the proportion of nitrogen present was approxi- 

 mately that in which it occurs in atmospheric air, though in 

 some instances it appeared that it was the only gas present ; 

 but these observations require confirmation. 



We have now concluded the consideration of the absorp- 

 tion and distribution of the various substances which are 

 absorbed by plants, and we will proceed, in the next lecture, 

 to study their relation to the metabolic processes. 



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