Respiration, Digestion, and Fermentation. 103 



the last marks made on the tube. Now carefully pour in 

 water from a graduated burette to fill the tube up to the 

 first mark made. The amount of water used from the 

 burette will then represent the volume of carbon dioxide 

 given oflE by the seeds and absorbed by the potassium. The 

 results are only generally approximate, and rest upon the 

 supposition that the amount of carbon dioxide given off and 

 the oxygen absorbed by the seeds are equal, which is not 

 always true. (Fairly accurate volumetric methods for respi- 

 ration are given in " Practical Text-book of Plant Physi- 

 ology.") 



Respiration tubes may be used also in this test. In this 

 case both the potash and water may be introduced into the 

 lower end of the tubes after the preparation is set up. 



106. Incomplete oxidation of oily seeds Soak a 



handful of oily seeds, such as those of hemp, in water for an 

 hour, and put in apparatus described above, from which the 

 potassium solutions have been omitted. Note the behavior 

 of the seeds, as indicated by the level of the mercury in the 

 tube. A decrease in the volume of the air in the tube or re- 

 tort would denote the absorption of one or more of the gases 

 by the seeds, with an exhalation not equal to it in amount 

 (§103). Note rise and fall of column. When the col- 

 umn returns to its original level, introduce the potassium 

 solution, and ascertain whether an exhalation of carbon 

 dioxide has begun. Describe the course of respiration in 

 oily seeds. 



107. Respiration without external oxygen. — Soak 

 a few peas in water for a day. Fill a five-inch test tube with 

 mercury; invert, and support with its lower end immersed in 

 a small dish of mercury. Select five sound peas, take off 

 the outer coating, and slip under the edge of the tube, and 

 allow them to rise to the top of the tube. Introduce a small 

 wad of filter paper in the same manner. Care must be taken 



