88 PLANTS MAKE FOOD 



Observations. — Do both lots of leaves show the presence of 

 starch ? 



Conclusion. — What is another factor necessary for the manu- 

 facture of starch in green leaves? 



* Problem 72 : The need of chlorophyll for starch making. 



Materials. — Coleus or other plant with variegated leaves, iodine, 

 methyl alcohol. 



Method. — Place the plant in full sunlight for an hour or two. 

 Test these several leaves with iodine after removing chlorophyll 

 with methyl alcohol. 



Observations. — Do all the leaves show the presence of starch? 

 Do all parts of the variegated leaves show starch ? 



Conclusion. — Is chlorophyll necessary for starch making? 



Problem 73 : To consider the leaf as a manufactory. 



NOTE. — Starch is made of the elements carbon, oxygen, and hydrogen. We 

 have seen that the roots of a plant take up soil water and we have found holes in 

 the leaves through which gases of the air might enter. Water (H 2 0) would account 

 for the hydrogen and oxygen, and carbon dioxide (CO2) will furnish the carbon and 

 oxygen. Let us compare the leaf with a mill for making starch. The sun furnishes 

 the energy to run the mill and the chlorophyll grains are the millstones. Carbon 

 dioxide and soil water are the raw products put into the mill. 



Observations. — Study figures on pages 92, 93, Civic Biology. 



1. What is the source of the water used in the leaf ? 



2. Where does the carbon dioxide come from? Trace it back 

 to its manufacture. 



3. What does the sun have to do with the work of a leaf? 

 Conclusion. — Write a paragraph telling how starch is made 



in a leaf. Use the terms machinery, raw materials, manufac- 

 tured products. 



Problem 74: To show that a gas is given off as a waste 

 product when green plants make starch. 



Materials. — Elodea, glass jar, funnel, test tube. 



Method and Observations. — Place some Elodea under a funnel 

 in fresh water. Then invert a test tube filled with water over the 

 funnel. See that the tube of the funnel is completely filled with 



