86 



Plants and their Ways in South Africa 



sets energy free to do work. Ask some one who plays football 

 how much weight the team loses while playing a cup match. 

 The stroke oar in a rowing match will lose six or seven pounds 

 in twenty minutes or during a four-mile race. How hard you 

 breathe when you are playing. Did you ever try to get warm 

 by breathing deeply ? A plant loses weight and gives off heat 

 in respiring ; it also gets energy to do work. 



Ex. 36. Place some peas that have just started germinating in a U- 

 tube. Cork tightly. Place the other end in a glass of pyrogallic acid. 



Ill 



FIG. 79. Peas germinating, deprived of oxygen. 



Since pyrogallic acid absorbs oxygen, the peas are deprived of the gas 

 necessary for respiration. The peas make no further progress in germina- 

 tion. In Fig. 79 the first jar contains water, the second caustic potash, 

 which absorbs CO 2 , the third pyrogallic acid. 



Ex. 37. Dissolve a few grains of methylene blue in a test tube of 

 water, using only sufficient to make a bright but transparent fluid. Place 

 within the solution some germinating seeds and observe on the following 

 day. The fluid has become transparent as the germinating seeds have 

 deprived the dye of its oxygen. Pour off some of the fluid into a flask 

 and shake vigorou ly. As the fluid mingles with ths air in the flask 

 its colour is partially restored. 



In a similar manner make a solution using this time methyl blue and 

 taking care as before not to have too deep a colour. Heat this fluid until 

 it becomes colourless and then breathe into it until the colour is restored. 

 Heating the fluid causes carbonic acid gas to expand and escape ; breath- 

 ing the gas into this fluid restores the colour. Now heat the fluid a second 



