88 The Living Plant 



piration, and examine more closely the chemical and physical 

 aspects thereof. Since the plant, in this process, absorbs oxygen 

 only, but releases carbon dioxide, a question is raised as to the 

 source of the carbon. This must come, of course, from some of 

 the innumerable carbon-holding compounds inside of the plant, 

 but, for our present purpose it does not much matter from which, 

 since they all are derived by transformation from the basal 

 grape sugar manufactured in the leaves. This grape sugar, ac- 

 cordingly, is the ultimate, even though not the immediate source 

 of the respiratory carbon. Therefore we can state the end prod- 

 ucts of respiration in this wise : — 



In respiration CgHioOg and O2 form CO2 and H2O 

 grape sugar oxygen carbon dioxide water 



This general statement can be given a definite chemical form 

 by making the two sides sum up alike, which requires these pro- 

 portions : — 



CeHi^Oe + 6 O2 = 6 CO2 + 6 H2O 



Now although this equation is rarely if ever actually realized 

 in any particular case, (respiration being never so simple, but a 

 process highly comphcated in its details), it does represent the 

 facts as to the ultimate materials and products, the two extremes 

 of the process; and accordingly we may place it in our series of 

 conventional constants as the respiratory equation. And its 

 relations to the photosjmthetic equation will not escape the notice 

 of the observant reader. The two are the exact reciprocals of 

 one another, which fact is one of the most consequential in all 

 nature, as will presently appear. 



And now we come to a matter which I wish to impress, the 

 strongest I can, on the mind of the reader. The phenomena we 

 have thus far considered, including the one which stands for 

 most people as the very embodiment of the process, viz., — the 

 remarkable exchange of the gases, — are by no means the ones of 

 greatest importance in respiration, but are secondary and in- 

 cidental to the central and crucial object of the process, which 



