RESPIRA TION. 



95 



that oxygen has entered, we may use the vessel for another experiment, 

 or set up a new one to be used in the course of 12 to 24 hours, after the oxy- 

 gen has been consumed. Place some folded damp filter paper on the ger- 

 minating peas in the jar. Upon this place one-half dozen peas which have 

 just been germinated, and in which the roots are about 2O-2$in>n long. See 

 figures 73, 74. The vessel should be covered tightly again and set aside in a 



Fig. 73- 



Fig. 74- 



Fig. 



Fig. 73. Seedlings in vessels containing an excess of carbon dioxide, and very little 

 oxygen. No growth takes place. 



Fig. 74. Vessel with normal air used as a check. No excess of carbon dioxide, usual 

 amount of oxygen. Normal growth takes place. 



Figures 73^ and 740. represent the condition of the peas in the experiment shown in figs. 

 73 an d 74. a month later. The cylinders as set up for that experiment were left fora 

 month and then photographed. The peas in the cylinder containing normal air have 

 grown, producing stems which reach to the top of the cylinder, while in fig. 73^, where 

 the oxygen was absent, the peas have died. At this time a test was made with a lighted 

 taper; it burned brightly in the cylinder 74^, but was quickly extinguished in the cylinder 

 73. The peas having died in this jar, decomposition had taken place and other gases than 

 carbon dio.xide were present, but there was not sufficient oxygen to support combustion. 



warm room. A second jar with water in the bottom instead of the germinat- 

 ing peas should be set up as a check. Damp folded filter paper should be 

 supported above the water, and on this should be placed one-half dozen peas 

 with roots of the same length as those in the jar containing carbon dioxide. 



