THE PHYSIOLOGY OF NUTRITION 



127 



bottle with a tight-fitting cork, and keep the Peas warm for two clays. 

 Note 



(i) That when the cork is removed and a lighted taper put in, the 

 flame is extinguished. 



(ii) If a little lime-water is shaken in the bottle, it turns milky. 



(iii) This shows that some or all of the oxygen has been used up by 

 the germinating seeds, and that carbon dioxide has been given out. 



EXPT. 117. Place a few Peas on damp cotton- wool at the bottom 

 of a bottle, and also place in the bottle a test-tube which contains a 

 solution of caustic potash. Through 

 the cork pass a glass tube bent into the 

 shape of a U, as is shown in Fig. 147, 

 and in the glass tube pour a little 

 coloured fluid. Note 



(i) The liquid stands at the same 

 level in both arms of the tube. 



(ii) As the experiment goes on, the 

 liquid rises in the arm of the tube which 

 is in direct contact with the air in the 

 bottle. 



(iii) The rise of the liquid is due to 

 the oxygen in the bottle being used up 

 by the germinating Peas, and the carbon 

 dioxide which they give out being ab- 

 sorbed by the caustic potash. The 

 pressure in the bottle being less than 

 the pressvire of the external air the liquid 

 is forced towards the bottle. 



(iv) At the close of the experiment 

 the caustic potash tube can be weighed, 

 and it will be found to have increased 

 in weight. 



FIG. 147. Diagram illustrating 

 how germinating Peas use up 

 oxygen and give out carbon 

 dioxide. A, B, level of co- 

 loured liquid ; C, D, the 

 change in level due to oxygen 

 being used. The carbon di- 

 oxide is absorbed by the caus- 

 tic potash in the test-tube. 



EXPT. 1 1 8. Obtain two Potato 



tubers of the same weight. Place one to dry in a hot oven, and the 

 other in a damp dark room. Examine both from time to time, and 

 note 



(i) The one in the oven, because water is driven off, loses weight. 

 When it is perfectly dry, weigh it, and record the change in weight. 



(ii) The one in the damp dark room commences to grow and pro- 

 duces small pale leaves and small tubers. 



(iii) After a time growth ceases, because the reserve material in the 

 tuber has been used up. 



(iv) Now take the old tuber, with the stems, leaves, and tubers which 

 have been produced, and place them in a hot oven until all the water 

 has been driven off. 



(v) Weigh the dry residue. It is lighter than the residue obtained 

 from the first tuber dried in the oven. This loss of weight is due to 

 respiration. During the whole of the time of growth, oxygen was taken 



