56 



PHYSIOLOG Y. 



130. Respiration is necessary for gr.owth. — 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 some 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 n^™ 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 Pfa seedlings ; Hie one 



. _ at ttie left had no oxygen 



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



first jar, while in the second one we see that the S, 'oxygen and grow^h"was 



roots have elongated considerably, if the experi- evident. 



ment has been carried on carefully. Therefore 



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



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



132. 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 i 

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

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



133. Respiration 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 contain- 

 ing baryta water. A similar 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 experi- 



Fig 49 ment. The bell jar containing the plant should be 



dio'xfdVfr^oXtTlant d"riSg covered with a black cloth to prevent carbon assi- 



respiration. Baryta water in milation. In the course of ten or twelve hours, if 

 smaller vessel. (Sachs ) 



