THE PHYSIOLOGY OF NUTRITION 



added to the solution the plant changes its colour and becomes 

 green. In fact, if some of the leaves are simply washed with a 

 weak solution of iron they turn green. 



When potassium nitrate is left out of the solution the plant is 

 stunted in its growth. 



EXPT. 106. Weigh a Turnip and place it in a hot oven for a few 

 days, or until it is perfectly dry. Weigh again, and note the change in 

 weight. The water in the Turnip has been driven off, and only the 

 solid matter remains behind. 



EXPT. 107. Twist a piece of stout iron wire many times round two 

 or three inches of a small branch, and burn the wood over a Bunsen or 

 spirit flame upon a plate. Note 



(i) The residue of incombustible matter (the ash). 



(ii) The bark produces the most ash. 



(iii) The colour of the ash is white or grey. 



EXPT. 108. Burn a piece of dry wood in a jar full of air. This can 

 be done by twisting a piece of wire round the wood to hold it with ; 

 then light the 

 wood and hold it 

 in the jar as long 

 *as it will smoul- 

 der. Pour into 

 the jar a little 

 lime - water. 

 Note 



(i) The lime- 

 water in the bottle 

 is clear and co- 

 lourless. 



(ii) The lime- 

 water becomes 

 milky when 

 shaken in the jar. 



(iii) This being 

 the test for carbon 

 dioxide, shows 

 that when wood is 

 burnt in air, car- 



bon dioxide 

 formed. 



FIG. 143. Water Culture. No. i. Pea plant grown in normal 

 solution. No. 2. Pea plant grown without jxrtassium. 

 No. 3. Pea plant grown without nitrates or ammonium 

 salts. No. 4. Pea plant grown with soda instead of 

 potash. No. 5. Pea plant grown without calcium. 



EXPT. 109. 

 Germinate a few 



Peas in damp sawdust. Obtain five wide-mouthed bottles with corks 

 and split the corks so that the plants can be suitably fixed. When the 

 Pea seedlings have their radicles about two inches in length, wash 

 them in pure water and fix five of the best developed in slits in the 



