RESPIRATION. 55 



129. If we now take some of the lime water and blow our 

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

 dioxide which we exhale unites with the lime in the water, and 

 forms carbonate of lime, 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 

 respiration. The oxygen in the vessel was used up in the proc- 

 ess, and carbon dioxide was given off. (It will be 1 seen that 

 this process is exactly the opposite of that which takes place in 

 carbon conversion. ) 



130. Respiration is necessary for growth. — After we have performed this 

 experiment, if the vessel has not been open too long so that oxygen has en- 

 tered, we may use the vessel for another experiment, or set up a new one to 

 be used in the course of 12 to 24 hours, after all the oxygen has been con- 

 sumed. Place some folded damp filter paper on the germinating peas in the 

 jar. Upon this place one -half dozen peas which have just been germinated, 

 and in which the roots are about 20-25 mm long. The vessel should be cov- 

 ered tightly again and set aside in a warm room. 

 A second jar with water in the bottom instead 

 of the germinating peas should be set up as a 

 check. Damp folded filter paper should be sup- 

 ported above the water, and on this should be 

 placed one-half dozen peas with roots of the 

 same length as those in the jar containing carbon 

 dioxide. 



131. In 24 hours examine and note how much Fig. 48. 



growth has taken place. It will be seen that the P« f e ,! d i in f s; the one 

 5 v at the left had no oxygen 



roots have elongated but very little or none in the and little growth took 

 r- . . ,-,.,, i ,. . ., place, the one at the right 



first jar, while in the second one we see that the in oxygen an d growth was 



roots have elongated considerably, if the experi- evident. 



ment has been carried on carefully. Therefore 



in an atmosphere devoid of oxygen very little growth will take place, which 



shows that normal respiration with access of oxygen is necessary for growth. 



132. Energy Bet 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 



