PLANTS IN RELATION TO SOIL, LIGHT, AIR 63 



Q. Plants Use Carbon Dioxide. — Light a short piece of candle 

 and fasten it with some of its own melted wax to a flat piece of cork 

 or light wood so it will float upright on water. Tie to the candle a, 

 string two feet long. Set it in a pan of water and invert an open 

 fruit jar just above it with the edges of the jar in the water. The 

 candle will burn only a short time, and the flame goes out for lack 

 of oxygen. The oxygen has been partly converted into carbon dioxide 

 by the burning of the carbon in the candle. Now remove the candle 

 by pulling it through the water by means of the string, allowing no 



Fig. 40. — Potato tubers sprouted in light (left) and in the dark (right). The 

 left one is plump, green, and the sprouts are more abundant. The right one is 

 shrunken, and the sprouts are fewer and longer. The tubers may well be exposed 

 to light for many days just before planting. (Productive Farm Crops.) 



fresh air to enter the jar. Introduce a leaf or two of geranium or 

 other window plant. A cork float may be used in keeping the leaf 

 surface above water. The stems should remain in the water to keep 

 them fresh. Now place the dish where the bright sun may strike 

 the leaves through the jar. After two days remove the leaf and test 

 the air by burning a candle in it. The burning, even for a short 

 time, vpill prove that the action of the leaf in the sunlight broke up 

 some carbon dioxide and left oxygen in its place. 



When plants are growing in daylight they use up the 

 carbon dioxide of the air and leave the oxygen. This in 



