RESPJRA TION. 



"3 



227. Respiration is necessary for growth. — After performing experiment in 

 paragraph 221, it the vessel has not been open 

 too long so that oxygen has entered, we may use 

 the vessel for another e.xperiment, or set up a 

 new one to be used in the course of r2 to 24 

 hours, after some oxvgen has been consumed. 

 Place some folded damp filter paper on the 

 germinating peas in the jar. Upon tliis place 

 one-half dozen peas which have just been 

 germinated, and in which the roots are about 

 20-25 """ 'ong- The vessel should be covered 

 tightly again and set aside in a warm room. 



Fig. 104. 



Pea seedlings; the one 



at the left had nu oxygen 



and little growth took 



place, the one at the right 



A second jar with water in the bottom instead in oxygen and growth 



- , . . 1111 . was eWdent. 



of the germinatmg peas should be set up as a 



check. Damp folded filter paper should be supported 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. 



228. In 24 hours examine and 

 note how much growth has taken 

 place. It wdU be seen that the 

 roots have elongated but very little 

 or none in the first jar, while in 

 the second one we see that the 

 roots have elongated consider- 

 ably, if the e.xperiment has been 

 carried on carefully. Therefore 

 in an atmosphere devoid of oxygen 

 very little growth will take place, 

 which shows that normal respira- 

 tion with access of oxygen (aerobic 

 respiration) is necessary for growth. 



229. Another way of perform- 

 ing the experiment. — If we wish 

 we may use the following experi- 

 ment instead of the simple one 

 indicated above. Soak a handful 

 of peas in water for 12-24 hours, 

 and germinate so that twelve with 

 the radicles 20-25 '""^ ^o^^g ^^J 



Fig. 105. 

 Experiment to show that growth takes 

 place more rapidly in presence of oxygen 

 than in absence of oxygen. The two tubes 

 in the vessel represent the condition at the 

 beginning of the experiment. At the close 

 of the experiment the roots in the tube at 

 the left were longer than those in the tube 

 filled at the start with mercury. The tube 

 outside of the vessel represents the condi- 

 tion of things where the peas grew m ab- 

 sence of oxygen; the carbon dioxide given 

 off has displaced a portion of the mercury. 

 This also shows anaerobic respiration. 



be selected. Fill a test tube with 

 mercury and carefully invert it in a vessel of mercury so that there will 



