RECENT RESEARCHES ON THE RESPIRATION OF PLANTS. 217 



because the first forms a soluble salt, and acts more efficaciously 

 on the carbonate. 



The following table shows the conditions in which the plants 

 were placed, and the volume of acid obtained; but which does 

 not, for the reason already given, represent the wliole of that 

 which was fixed. 



Although the exhalation of carbonic acid under the influence 

 of the solar rays at a certain temperature cannot be doubted, it 

 must nevertheless be admitted that in the young shoots and 

 leaves there exist two simultaneous and opposed actions, one of 

 combustion, the other of reduction, and that the accumulation of 

 carbon in plants can only be explained by the greater effect of 

 the latter as compared with that of the former. New experi- 

 ments upon this matter were however required in order that this 

 curious subject might be satisfactorily understood, and they have 

 accordingly been made. Tiiey were suggested by the following- 

 consideration : if plants exhale carbonic acid at the very same 

 time that they reduce it, they ought incessantly to reduce that 

 which they give oflf if they are in a confined atmosphere. If 

 then two branches covered with green leaves, of tlie same plant, 

 of equal ages and weights, were placed in two equal atmosphera*;, 

 one with and the other without a solution of baryta, the glass 

 with baryta-water ought to contain more carbonic acid than the 

 other, inasmuch as the gas would be fixed in the former, and 

 thus not be liable to be reduced by the leaves. 



The following table shows the results obtained by actual 

 experiments, and the conditions under which they were ob- 

 tained. 



