166 GREEN PLANTS AS FOOD MAKERS 



Practical Exercise 11. Fill out the following table on the work of the leaf. 



Pabt 



Function 



What Happens 



What Causes It to Happen 











Self-Testing Exercise 



Green plants manufacture (1), (2), and 



(3). The manufacture of (4) by green plants in the presence 



of sunlight is called (5) . (6) is not a necessary 



factor for protein-making. In order for food to circulate from one 



part of the plant to another, the (7) food must be made 



(8). This change is caused by (9), and is known as 



(10). Food is needed for (11) and (12). 



Green plants give off (13) (14), (15) t and 



(16). 



PROBLEM IX. HOW IS FOOD CIRCULATED IN A PLANT? 



The circulation and final uses of food in green plants. We 



have seen that cells of green plants make food — especially the 

 cells that are in the leaves. But all parts of the bodies of plants 

 grow. Roots, stems, leaves, flowers, and fruits grow. Seeds 

 are storehouses of food. We must now examine the stem of some 

 plant in order to see how food is distributed, stored, and finally 

 used in the various parts of the plant. 



The structure and growth of a dicotyledonous or woody stem 

 If we cut a cross section through a young willow or apple stem, we 

 find it shows three distinct regions. The center is occupied by 

 the spongy, soft pith; surrounding this is found the rather tough 

 wood, while the outermost area is bark. More careful study of the 

 bark reveals the presence of three layers — an outer layer, epidermis, 

 a middle green layer, cortex, and an inner fibrous layer. The inner 

 layer is made up largely of tough fiberlike cells known as bast fibers. 



