HOW PLANTS DO THEIR WORK 295 



does this show as to where transpiration takes place more 

 rapidly ? 



We are now ready to find out something about the way 

 in which plants manufacture their products. To under- 

 stand this we must know something about leaves. 



Examine a leaf of any plant. What are its parts 

 stem or petiole, expanded portion or blade. Hold the leaf 

 between you and the light. What do you see in it ? How 

 are the veins arranged in a bean leaf, maple, sunflower ? 

 These are net- veined leaves. How are the veins arranged 

 in a corn leaf? In grass? These are parallel veins. What 

 is the use of the veins? By discussion the value of the 

 veins in holding the leaf spread* will be brought out. 

 Place a twig with growing leaves in a tumbler of water 

 colored with red ink. After twenty-four hours examine 

 the petiole, the veins. What do you conclude? If you 

 can procure a thick leaf, as live-for-ever, tulip, or hepatica, 

 have the pupils peel off a little of the skin or epidermis. 

 Even a thin leaf may have a little of the covering removed, 

 enough to lead the pupils to see that the entire leaf is 

 covered with a thin, almost transparent skin. What is"" 

 under the skin? This green, granular mass is chiefly 

 chlorophyll bodies. If the pupil could see a cross sectior 

 of a leaf highly magnified he would find it built up of cells 

 one layer above another. Each cell has a thin wall and 

 contains a number of green, roundish bodies called chloro- 

 phyll bodies, and a mass of colorless protoplasm. The 

 protoplasm is the living part of the leaf, and is the machin- 

 ery that manufactures the plant products. But just as 

 any machinery must have power to make it run, so must 



the protoplasm of the leaf. What is the power ? 

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