

HOW THE LEAF GETS FOOD FROM THE AIR 73 



made up are like tiny balloons with spaces between 

 them in which air may pass freely. All of them to- 

 gether expose a great surface for absorbing air. 



Why does the plant need so much leaf surface? Be- 

 cause there is so little food in the air (only one part in 

 about two thousand parts of air). In a room twenty 

 feet high, twenty feet wide, and forty feet long there is 

 only enough air food to make about one pound of 

 starch, and to make this in a day a leaf surface equal 

 to that of the whole floor of the room is needed. This 

 is only possible if the air of the room be stirred up the 

 whole time and the room have walls of glass through 

 which bright sunshine shines all day long. 



Why does the leaf need sunshine to make food? 

 From the sunlight we can get energy, or the power 

 which makes anything move. By means of a burning 

 glass placed in the sun we can make water boil and 

 cause a tiny engine to go. If we knew how to use the 

 energy of sunlight, we could run all our machinery by 

 it. The leaves can and do use it in making food. 

 We shall understand this better if we try a few experi- 

 ments. 



Is light needed for making starch? Pick some 

 leaves (those of nasturtium or English ivy are good) 

 near the close of a bright sunshiny day. Boil them 

 fifteen minutes in water and cover them with alcohol 

 (denatured alcohol or wood alcohol will serve). In the 

 morning pour off the alcohol and cover them with 



