132 NATURE TEACHING 



PRACTICAL WORK 



Burn some vegetable matter for instance, leaves or 

 twigs on a sheet of iron over a fire, or some wood in a 

 grate or stove. Notice that a large amount of the 

 material disappears, and that a comparatively small 

 amount of ash remains. This ash is the mineral matter 

 of the plant, the carbon and nitrogenous substances 

 having burnt away. 



Gently heat a fragment of wood, a little starch, a 

 lump of sugar, and a leaf, on a sheet of iron over a lamp 

 or fire. Notice that all of them blacken, thus indicating 

 the presence of carbon. If sufficient heat is applied the 

 carbon burns away, forming carbon dioxide and water 



(see p. 76). 



The Food of Plants. 



Take four ordinary flower-pots containing damp 

 sawdust, and sow in them seeds of barley, buckwheat or 

 other plants. Place all the pots in the dark until the 

 seeds have germinated. Now leave two pots in the dark, 

 and put the other two in a window where they obtain 

 plenty of direct sunlight. Water all as required. 



Make careful notes of the progress of the plants in 

 each case, noting whether they become green or not, 

 the growth each makes, and how long they live. 



The experiment may be made quantitative as follows. 

 Weigh out say a dozen seeds for each pot, before sowing, 

 and record their total weights. Allow the plants to 

 grow, and then when they have died pull them up 

 carefully, wash off any sawdust, and drylhem thoroughly 

 in the sun. Weigh the twelve plants from each pot, and 



