KESPIKATION 295 



to be barium carbonate. The formation of this body 

 proves the exhalation of carbon dioxide by the seeds, 

 as the entering air contains none. By separating and 

 weighing the barium carbonate precipitated in c, the amount 

 of the gas evolved in a definite time may easily be ascer- 

 tained. 



If the tubes between B and A and A and o be cut and 

 joined by a narrow india-rubber pipe which can be com- 

 pressed by a metal clip, the jar A can be isolated and the 

 carbon dioxide allowed to accumulate in it. 



These two processes, the absorption of oxygen and the 

 exhalation of carbon dioxide, are characteristic of what is 

 known as respiration. As already stated, it is a normal 

 process of the life of almost all protoplasm, and is con- 

 tinually going on so long as life lasts, although it is not 

 easily observed while the converse process, the absorption 

 and decomposition of carbon dioxide, is proceeding, accom- 

 panied by the exhalation of oxygen. It is frequently said 

 that during daylight the process of the respiration of a 

 green plant is masked by that of carbon dioxide decom- 

 position. To put this statement into somewhat different 

 terms, the carbon dioxide which is liberated in the course 

 of respiration by the green plant, and which is in com- 

 paratively small amount, is re-absorbed by the green parts 

 of the cells, and undergoes the same decomposition as that 

 which is brought to the plant by the surrounding air. It 

 thus escapes observation unless special means, such as 

 those detailed, are adopted to bring it into evidence. 



The respiratory processes are easily observed in the 

 case of all plants, and parts of plants, that are not green, 

 as there are in such cases no gaseous interchanges that 

 would interfere with their manifestation. 



If a plant be carefully weighed at the commencement 

 and at the end of such an experiment as has been described, 

 it will be found to have lost weight during its stay in the 

 receiver, so that respiration is associated with a loss of 

 weight to the plant. This may readily be inferred from 



