RESPIRA TION. 



Ill 



222. If we now take some of the baryta water and blow our 

 "breath" upon it the same film will be formed. The carbon 

 dioxide 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 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 res- 

 piration. 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 

 carbon-dioxide assimilation.) 



223. To show that oxygen from the air is used up while 

 plants respire. Soak some wheat for 24 hours in water. 

 Remove it from the water and place 



it in the folds of damp cloth or 

 paper in a moist vessel. Let it 

 remain until it begins to germinate. 

 Fill the bulb of a thistle tube with 

 the germinating wheat. By the aid 

 of a stand and clamp, support the 

 tube upright, as shown in fig. 102. 

 Let the small end of the tube rest 

 in a strong solution of caustic potash 

 (one stick caustic potash in two- 

 thirds tumbler of water) to which 

 red ink has been added to give a 

 deep red color. Place a small glass 

 plate over the rim of the bulb and 

 seal it air-tight with an abundance 

 of vaseline. Two tubes can be set 

 up in one vessel, or a second one 

 can be set up in strong baryta water 

 colored in the same way. 



224. The result. It will be seen that the solution of caustic 

 potash rises slowly in the tube; the baryta water will also, if 

 that is used. The solution is colored so that it can be plainly 



Fig. 102. 





