Respiration, Aeration, and Fermentation 283 



This may not be practicable for the present purpose, and 

 a simple suggestion of these gas relations is brought out 

 by means of the often misused experi- 

 ment with germinating seed. In this 

 experiment the seed are placed in 

 two bottles or jars carefully corked 

 or sealed. After the lapse of a few 

 hours a lighted taper lowered into 

 one jar will be extinguished, and at 

 the same time a thick film of barium 

 carbonate will form on baryta water 

 in a dish introduced into the other 

 jar. (This film is far more pro- 

 nounced than that which would form 

 upon a similar test in a control jar 

 containing air.) 



The above experiment suggests 

 definitely two things : (1) that the 

 content of CO 2 has been increased, 

 and (2) that oxygen has disappeared ; 

 but neither this nor any other sim- 

 ple experiment, unfortunately, af- 

 fords convincing proof that no FlG . 69 . simple respiro . 

 other change takes place. scopes. 



A far better demonstration of the evolution of carbon 

 dioxid is obtained by employing growing seeds in other 

 types of apparatus, two of which may be briefly referred 

 to : (1) by germinating seeds in a bottle or test-tube over 

 baryta water (Fig. 69), or in a chamber in which a dish 

 of baryta water is placed, and by comparing the amount 

 of the precipitate in this respiration chamber with that in 



