A STUDY OF FOODS 47 



printed label, should be able to determine exactly what he 

 is paying for and putting into his body. 



3. How PLANTS MANUFACTURE FOOD MATERIALS 



Carbohydrates. A glance at Fig. 13 shows that carbohy- 

 drates are found almost wholly in foods of vegetable origin. 

 These starches and sugars are probably the simplest form 

 of organic food manufactured by plants. We shall now try 

 to understand something of the method by which plants 

 carry on their all-important work. 



Organs of a Plant. The common plants with which we are 

 familiar for example, dandelions, and maple trees consist 

 of three important organs, namely, roots, stems, and leaves. 

 The root system is usually found beneath the ground, 

 firmly holding the plant to the soil. Stems, on the other 

 hand, commonly rise into the air in a more or less vertical 

 direction, and serve as a means of connection between the 

 roots below and the leaves that are attached along the sides 

 and at the top of the plant. If one cuts off from a .living 

 plant a small leafy branch, and puts the lower end of the 

 stem into red ink, he will see after a time traces of the red 

 ink in the veins of the leaf; and if the experiment is success- 

 ful, every one of the fine branches of the veins will at last 

 be filled with the colored fluid. Cross and longitudinal sec- 

 tions of the stem will show that the red ink has been carried 

 up through little tubes called ducts. If pieces of root are 

 experimented upon in the same way, similar ducts will be 

 found. We can demonstrate in this and in other ways that 

 there is a continuous system of ducts, beginning at the tips 

 of the roots, running up the stem, and branching out into 

 the leaves. By this means water and the mineral matters 

 dissolved from the soil are carried up the stem and supplied 

 to the leaves. 



Leaves, as we all know, are usually green in color. When 

 we examine the cross section of a leaf under the microscope, 



