RESPIRATION 89 



seeds especially give off a large quantity of carbon dioxid. 

 In a wide-mouthed bottle place several hundred germinating 

 pea seeds. Fill a small vial with a filtered concentrated 

 solution of barium hydrate. Place the vial in the bottle 

 with the seeds. Do not spill the solution. Tightly stopper the 

 wide-mouthed bottle and after several hours note the heavy, 

 white precipitate that forms in it. As a check, place a 

 similar vial of barium hydrate solution is a similar bottle 

 tightly stoppered. Does a heavy precipitate form? Using 

 a piece of glass tubing, blow air into a bottle of barium hy- 

 drate. The exhaled air is rich in carbon dioxid. The water 

 becomes turbid, due to the precipitate formed when carbon 

 dioxid reacts with barium hydrate. 



Review. — What are the sources of the raw material? What part 

 of the dry matter is carbon? What percentage of the air is carbon 

 dioxid? How does it enter the plant? W T hat is chlorophyll? What is 

 necessary for its formation? What is meant by photosynthesis? What 

 gas is given off in photosynthesis? What conditions are necessary for 

 photosynthesis? What is meant by digestion of starch? What is meant 

 by assimilation? Respiration? When does it occur? What gas is given 

 off in the process? What gas is required in the process? Contrast the 

 process of respiration in animals and plants. 



