RESPIRATION 289 
analysis shows 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 
ascertained. 
If the tubes between 8 and a and a and c 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. 
Tia 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 
19 
