368 CHANGES OF ORGANIC MATTER IN THE PLANT. 



air supplied to ttie seeds in the bell-jar, of course first carefull3' 

 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 in 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 bj' any 

 plant under the conditions to whicli ordinary house-plants are 

 subjected is represented Ijy 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. • 



972. 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 tlie exact relations of volume of the absorbed oxjgen 

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

 certain cases the amount of carbonic acid e\'olved is less than 

 would be expected from tlje 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 starchj' seeds. Hellriegel has shown that in 

 one instance the fixation of oxygen amounted to an increase in 

 weight of 1.15 percent. 



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

 ratory process. Saussure-' has shown that the amount in tlie 

 atmosphere can even be reduced one half without materiallj' 

 interfering with the functions of the plant. 



Most observers have found that in pure oxygen there is an 

 increase in the activity* of the respirq,tory function. 



Bert'' has conducted interesting experiments upon the effect 



1 Quoted hy Pfcirer, Pllanzenphyslologie, i. p. 373. 



^ For a discussion of this question, particularly witli reference to tlie lower 

 organisms, consult Bert : La pression baromfetrique, 1878- 



