I04 



Elementary Plant Physiology. 



that no air is introduced in the operations mentioned. Ob- 

 serve twelve and twenty-four hours later. 



Test the gas exhaled by the seedlings, by pushing a small 



stick of potassium hydrate 

 under the edge of the tube 

 as before. If it absorbs the 

 gas, and the mercury again 

 rises to the top of the tube, 

 it will demonstrate that 

 the seeds of the pea are 

 capable of carrying on 

 respiration without ex- 

 ternal oxygen, exhaling 

 carbon dioxide during the 

 process. 



io8. Influence of 

 temperature upon res- 

 piration — Set up two ex- 

 periments as above, fixing 

 the tubes firmly in place. Now leave one to endure ordinary 

 room temperatures, and set the other one in a large pail or 

 dish. Pour water into the pail until the test tube is com- 

 pletely immersed, then put several large pieces of ice into 

 the water. Add more ice as needed, and note the temperature 

 of both preparations four or five times during the next twelve 

 hours. Compare the amount of gas given off as denoted 

 by the fall of the mercury column in the test tube. The 

 actual amount of gas exhaled in the above tests may be found 

 by marking the limits of the column of gas in the tube, and 

 then afterward noting the amount of water taken from a 

 graduated burette to fill the tube to the levels indicated. 

 Repeat the tests given above, using wheat or corn, and 

 ascertain if these seeds may also carry on respiration 

 by this method. What is the difference in chemical corn- 



Fig. 77, — Liberation of carbon dioxide 

 witliout external oxygen. 



