202 PHYSIOLOGICAL BOTANY. PART II. 



that the decomposition of this gas by the direct Gyr- 

 ation of the vital principle furnishes the first step to- 

 wards the organisation of brute matter. 



The ultimate effects of vegetable respiration being the 

 reverse of those which result from the analogous func, 

 tion in animals, have been often regarded as a remark- 

 able provision against the gradual deterioration of our 

 atmosphere. But the effects produced by the respiration 

 of animals, by combustion, and by various other processes 

 by which carbonic acid is added to the atmosphere, are 

 of too trifling a description to enable us to appreciate 

 their consequences under the lapse of many ages. The 

 continued spontaneous decomposition of a large portion 

 of dead vegetable matter, is also perpetually counter- 

 acting some portion of the beneficial effects which the 

 fixation of carbon by plants might produce. Still it 

 is evident that every particle of carbon in living vege- 

 tables, and likewise all that exists in those fossil bodies, 

 coal, jet, &c. which are the altered remains of primaeval 

 vegetation, must have resulted from the decomposition of 

 carbonic acid whose oxygen has been set free during 

 the process of vegetable respiration. To this we may 

 also add whatever carbon is found in animals, since 

 this has been derived from their food primarily ob- 

 tained from the vegetable kingdom. We should possess 

 something like a measure of the extent to which vege- 

 tation has been active in altering the state of our atmo- 

 sphere, if we could obtain an estimate of how much 

 oxygen would be required to convert into carbonic acid 

 all the carbon now fixed in organised beings, recent and 

 fossil ; and hence we might ascertain whether the at- 

 mosphere thus modified would still be fitted for our 

 respiration or not. But in other respects there can be 

 no doubt of the important results to which the respiration 

 of vegetables gives rise. It is this process which pre- 

 pares the organisable materials from whose subsequent 

 elaboration are derived those infinitely varied conditions 

 of organised matter which are essential to the develop- 

 ment of the numerous tribes of plants which gladden 



