CHAPTER XVI. 



RESPIRATION. 



Exercise 33. 



166. Simple experiment to demonstrate the evolution of C0 a during 

 germination. — Where there are a number of students and a number of large 

 cylinders are not at hand, take bottles of a pint capacity, place in the bottom 

 some peas soaked for 12 to 24. hours. Cover with a glass plate which has 

 been smeared with vaseline to make a tight joint with 

 the mouth of the bottle. Set aside in. a moderately 

 warm place for 24 hours. Then slide the glass plate 

 a little to one side and quickly pour in a little baryta 

 water so • that it will run down on the inside of the 

 bottle. Cover the bottle again. Note the precipitate 

 of barium carbonate which demonstrates the presence 

 of C0. 2 in the bottle. Lower a lighted taper. It is 

 extinguished because of the great quantity of CO a . 



Exercise 34. 



167. Comparison of respiration in plants and ani- 

 mals — Take some of the baryta water and breathe 

 upon it. The same film is formed. The carbon diox- 

 ide which we exhale is absorbed by the baryta water 

 and forms barium carbonate, just as in the case of the 

 peas. In the case of animals the process by which ( Sacl >s.) 

 oxygen is taken into the body and carbon dioxide is given off is respiration. 

 The process in plants which we are now studying is the same, and also is 

 respiration. The oxygen in the vessel was partly used up in the process and 

 carbon dioxide was given off. (It will be seen that this process is exactly the 

 opposite of that which takes place in starch formation.) 



Exercise 35 (or Demonstration). 



168. Respiration is necessary for growth. — After we have performed the 

 experiment in paragraph 166, if the vessel has not been open too long so 



94 



Fig. 72. 

 Test for presence of 

 carbon dioxide in vessel 

 with germinating peas. 



