58 



PHYSIOLOGY. 



peas the taper burned brightly, while in the other jar the flame was quickly 

 extinguished. In this jar, while there was very little or no oxygen, there were 

 present other gases than carbon cioxide because putrefactive processes were 

 now going on in the large mass of peas in the jar. 



138. Another way of performing the experiment. — If we wish we may 

 use the following experiment instead of the simple one mdicaied above. 



Soak a handful of peas in water 

 for 12-24 hours, and germinate 

 so that twelve with the radicles 

 2o-25«/;« long may be selected. 

 Fill a test tube with mercury 

 and carefully invert it in a ves- 

 sel of mercury so that there will 

 be no air in the upper end. 

 Now nearly fill another tube and 

 invert in the same way. In the 

 latter there will be some air. Re- 

 move the outer coats from the peas 

 so that no air will be introduced in 

 the tube filled with the mercury, 

 and insert them one at a time under 

 the edge of the tube beneath the 

 mercury, iix in each tube, having 

 first measured the length of the 

 radicles. Place in a warm room. 

 In 24 hours measure the roots. 



Fig. 50. 

 Experiment to show that growth takes place 

 mure rapidly in presence of oxygen than in ab- 

 sence of oxygen. At the beginning of the experi- 

 ment the two tubes in the vessel represent the 

 condition at the beginning of the experiment. Those ill the air will h;ive grown 

 A*^ the close the roots in the tube at tlie left were 

 longer than those in the tube filled at the start 

 with mercury. The tube outside of the vessel 

 represents the condition of tilings where the peas 

 grew in absence of oxygen ; the carbon dioxide 

 given off has displaced a portion of tiie mercury. 

 This also shows intramolecular respiration. 



considerably, while those in the 

 other tube will have grown but 

 little or none. 



139. Intramolecular respira- 

 tion. — The last experiment is also 

 an excellent one to show what is called intrmnoleadar respiration. In the 

 tube filled with mercury so that when inverted there will be no air, it will be 

 ceen after 24 hours that a gas has accumulated in the tube wkicli has crowded 

 out some of the mercury. "With a wash bottle which has an exit tube properly 

 curved, some water may be introduced in the tube. Then insert underneath 

 a small stick of caustic potash. This will form a solution of potash, and the 

 gas will be partly or completely absorbed. This shows that the gas was car- 

 bon dioxide. This evolution of carbon dioxide by living plants when there is 

 no access of oxygen is called intramolecular respiration. It occurs markedly 

 in oily seeds and especially in the yeast plant. 



