114 PHYSIOLOGY. 



be no air in the upper end. Now nearly fill another tube and invert in the 

 same way. In the latter there will be some air. Remove the outer coats 

 from the peas so that no air will be introduced in the tube filled with the 

 mercury, and insert them one at a time under the edge of the tube beneath 

 the mercury, six in each tube, having first measured the length of the radicles. 

 Place in a warm room. In 24 hours measure the roots. Those in the air 

 will have grown considerably, while those in the other tube will have grown 

 but little or none. 



230. Anaerobic respiration. The last experiment is also an excellent 

 one to show anaerobic respiration. In the tube filled with mercury so tha; 

 when inverted there will be no air, it will be seen after 24 hours that a gas 

 has accumulated in the tube which has crowded out some of the mercury. 

 With a wash bottle which has an exit tube properly curved, some water 

 may be introduced in the tube. Then insert underneath a small stick of 

 caustic potash. This will form a solution of potash, and the gas will be 

 partly or completely absorbed. This shows that the gas was carbon di- 

 oxide. This evolution of carbon dioxide by living plants when there is no 

 access of oxygen is anaerobic respiration (sometimes called intramolecular 

 respiration). It occurs to a marked extent in the yeast plant. 



231. Energy set free during respiration. From what we have learned of 

 the exchange of gases during respiration we infer that the plant loses carbon 

 during this process. If the process of respiration is of any benefit to the 

 plant, there must be some gain in some direction to compensate the plant 

 for the loss of carbon which takes place. 



It can be shown by an experiment that during respiration there is a 

 slight elevation of the temperature in the plant tissues. The plant then 

 gains some heat during respiration. Energy is also manifested by growth. 



232. Bespiration in a leafy plant. We may take a potted plant which 

 has a well-developed leaf surface and place it under a tightly fitting bell jar. 



Under the bell jar there also should be placed 

 a small vessel containing baryta water. A sim- 

 ilar apparatus should be set up, but with no 

 plant, to serve as a check. The experiment must 

 be set up in a room which is not frequented by 

 persons, or the carbon dioxide in the room from 

 respiration will vitiate the experiment. The bell 

 jar containing the plant should be covered with 

 a black cloth to prevent carbon assimilation. In 



Test for Hberation of car- the course of IO or I2 hours > if everything has 

 bon dioxide from leafy plant worked properly, the baryta water under the jar 

 during respiration. Baryta .,, , -ni 1^1 r-L- 



water in smaller vessel, with the plant will show the film of barium car- 



(Sachs.) bonate, while the other one will show none. Res- 



piration, therefore, takes place in a leafy plant as well as in germinating seed* 



