FOODS AND WHERE THEY COME FROM 311 



thickened leaves. Buds and flowers are occasionally 

 used, cauliflower and Brussels sprouts being the most 

 common examples. 



Green Plants Make Food. We have said that green 

 plants make the food of the world. This is very easy to 

 show by means of an experiment. If we take a healthy 

 plant, such as a common geranium, and put it in the dark 

 for at least 24 hours, it will use up all the spare food made 

 in the leaves. While it is still in the dark, we may fasten 

 pieces of cork on some of the leaves. These pieces of 

 cork must be so placed that both sides of the leaf are 

 covered. We will then put the plant in strong sunlight 

 for a few hours. Later we can pick off the leaves which 

 have the cork on > 



them, remove the 

 cork, and boil the 

 leaves. Then we 

 place them in hot 

 methyl alcohol. 

 This takes the green 

 coloring matter out 

 of the leaves and 

 makes them appear 

 to be white. If we 

 now wash the leaves 

 carefully and then 

 put them in an 

 iodine solution, 1 we 

 will find that the 

 area covered by the 

 cork remains white while the rest of the leaf turns dark 

 blue or black. Iodine is a test for the presence of starch. 



1 Made by adding a few crystals of iodine to 95 per cent alcohol, or by 

 adding to one gram of iodine, two thirds of a gram of potassium iodide 

 and then adding enough 35 per cent alcohol to darken to a brown color 



this takes 

 rtva.te.r- cxna. expose "Co sun ou t the 



start VitVz a plant that 

 . has been in a ctark 

 closet for 24 hours. 



green 



