604 NATURE STUDY. 



the difference between the raw material used and the manu- 

 factured product, and on the necessity of machinery and of 

 an engine and furnace or other source of power. Tell 

 them that the leaves are starch factories worked by sun 

 power. Through the " breathing-pores " with which they 

 breathe they take in parts of the air ; through their roots 

 they take in water; and out of these make, with the help 

 of the sun, starch and other plant food. Like any other 

 factory they cannot work without power to make them go. 

 They only work in the daytime when they have the sun. 

 Hence we see why every leaf tries to get out vhere it can 

 see the sun and get sun power. Perhaps the children have 

 discovered that those leaves which cannot get the sunlight 

 turn yellow, and many finally die and drop off. 



In these factories are millions of minute green bodies, 

 each of which is a machine for making starch. When the 

 leaf does not get the sunlight, these starch machines lose 

 their green color and break down. Then the leaf loses its 

 green color, and may wither and die. 



What could plants do without leaves ? 



The Leaves as Air Purifiers. 



Beginning with the experiment of breathing into a paper 

 bag held tightly over mouth and nose, lead children to see 

 that the air in the bag gets " bad," because we have breathed 

 into our body the part of the air (oxygen) helpful to us, and 

 have breathed out into the bag gases poisonous to us (" car- 

 bonic acid "). But this poisonous gas, which we and all an- 

 imals breathe out, the leaves of the morning glory and of all 

 other plants take in, and out of it and water make starch. 

 So every leaf, as long as it has sun-power, is taking out of the 

 air this poisonous gas, and making the air more fit for us 

 and all animals to breathe. Nor is this all. In the process 

 of making starch every leaf is setting free and throwing out 



