CHAPTER XXXI 

 PLANT LIFE 



How Plants Work. You have seen how light and heat 

 and air and water and soil are related to our lives. Now, 

 the green plants must be added to our mental picture be- 

 fore we can really understand how we live. We must see 

 the green plants at work in the midst of these other things 

 and understand how they work. 



Think, then, of a young corn-plant. There it stands 

 alive and at work in the midst of millions of others. Its 

 leaves are spread to the sunlight while its roots burrow 

 in the dark among the soil grains. Somehow, from soil 

 and air, it gathers materials, transforms them into food, 

 and stores this food in the swelling grains. This is the 

 process we must try to understand. This is work that all 

 green plants do. It is work that animals cannot do; they 

 must depend upon plants for this great process of changing 

 inorganic substances into organic ones, the building up of 

 food. Plant bodies, like our own, cannot take in solid 

 materials. The substances that enter them must be in 

 either liquid or gaseous form. So the corn-plant takes in 

 liquids and gases. It also gives out gas in the form of 

 water vapor that evaporates from its leaves. It cannot 

 live without a constant income and outgo of materials. 

 Neither can we. 



Roots. The roots burrow deeply in the soil, and, near 

 their tips, they produce millions of delicate hairs called 

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