The Food-making of Plants 6g 



To show that no Starch is made without Carbon 

 Dioxide. — Cut under water two small shoots and place in 

 small vials of water. Lower the vials into wide-necked jars 

 and tie over the mouths of each some cloth net. Sprinkle over 

 one net a thick layer of soda-lime ; over the other a layer of 

 sand. In a day or two the plant under the soda-lime withers 

 and droops. A test for starch shows that none has been made. 

 The covering of soda-lime absorbs the CO2 and prevents any 

 from entering. Carbon dioxide was admitted into the one 

 covered simply wirti sand, and starch-making was unhindered. 



When carbon dioxide is supplied to the leaves of a plant, it 

 meets the water that has been drawn up from the roots. Water 

 is made of two parts of hydrogen and one part of oxygen (HoO). 

 The water and carbon dioxide mingle and form carbonic 

 acid (CH2O3). In the green of the leaf the carbon and hydrogen 

 and oxygen, warmed by the light of the sun, become very active. 

 They separate and come together until another compound, 

 sugar, is formed. The symbol for sugar is CgHioO,-,. To 

 make one part of sugar requires six parts of carbon dioxide to 

 supply sufficient carbon. But this provides twelve parts more 

 oxygen than is required, which passes off in the way we have 

 found. 



After sugar is formed, one part of water is given off, leaving 

 starch (C^HioOs). 



In making starch, plants give off the gas we require in 

 breathing. In breathing, plants and animals exhale the gas 

 which plants require for starch-making, carbon dioxide. 



Plants get all their energy for doing work from the sun. 



They require chlorophyll or green colouring matter for 

 making starch. 



