368 CHANGES OF ORGANIC MATTER IN THE PLANT. 



air supplied to the seeds in the bell-jar, of course first carefully 

 freed from every trace of carbonic acid, is drawn through by 

 means of an aspirator, and in the bulbs all the carbonic acid 

 derived from the germinating seeds is retained. 



971. Plants iii dwelling-houses. To what extent can house- 

 plants injure the air of rooms at night? The carbonic acid which 

 is given off by plants comes from the breaking up of assimilated 

 matters in the various activities of the organism, such as growth, 

 movements, etc. But the total amount of work done by any 

 plant under the conditions to which ordinary house- plants are 

 subjected is represented by the oxidation of a very small amount 

 of food. From the most trustworthy data it is safe to say that 

 in the case of one hundred average house-plants the whole 

 amount of carbonic acid resulting from such oxidation during 

 work would not vitiate the atmosphere of a moderate-sized room 

 to any appreciable extent ; in fact, would be exceeded by the 

 amount evolved from a common candle burning for the same 

 length of time. 



072. Relation of the carbonic acid given off to the oxygen 

 absorbed. Owing to the fact that part of the carbonic acid 

 produced during respiration is retained within the plant, and 

 that water is formed as a product of respiration, it is difficult to 

 determine the exact relations of volume of the absorbed oxygen 

 and the evolved carbonic acid. It is known, however, that in 

 certain cases the amount of carbonic acid evolved is less than 

 would be expected from the amount of oxygen absorbed. This 

 is well shown when the germination of oily seeds is compared 

 with that of seeds containing chiefly starch. When oily seeds 

 germinate, the amount of carbonic acid is appreciably less than 

 that given off by starchy seeds. Hellriegel has shown that in 

 one instance the fixation of oxygen amounted to an increase in 



/ ^j 



weight of 1.15 percent. 



973. The free oxygen of the atmosphere is ample for the respi- 

 ratory process. Saussure 1 has shown that the amount in the 

 atmosphere can even be reduced one half without materially 

 interfering with the functions of the plant. 



Most observers have found that in pure oxygen there is an 

 increase in the activity of the respiratory function. 



Bert 2 has conducted interesting experiments upon the effect 



1 Quoted by Pfeffer, Pflanzenphysiologie, i. p. 373. 



2 For a discussion of this question, particularly with reference to the lower 

 organisms, consult Bert : La pression barometrique, 1878. 



