CHAPTER XXIII 

 THE LIFE OF A PLANT 



295. Study of a Plant. We have learned that plants 

 and animals alike are characterized by certain life activities 

 or functions; namely, nutrition, reproduction, irritability, 

 and spontaneous motion. A common plant that can be 

 grown readily in a schoolroom will help us to understand how 

 plants are able to carry on these life activities. A bean plant 

 will illustrate the structure and the work of all green plants. 



If we examine a mature plant, we notice first that it has 

 several parts or organs. These are roots, stems, leaves, and 

 sometimes flowers. 



296. Roots. If we dig up a bean plant, we note how 

 firmly the roots anchor it to the ground and how the particles 

 of soil cling to the young rootlets. The central root, which 

 seems to be the downward continuation of the stem, is called 

 the primary root, and its branches are called secondary roots. 



297. Extent of Roots. The total length of the roots of 

 an ordinary plant is much greater than is commonly sup- 

 posed, for when a plant is pulled up, a large part of the whole 

 mass of roots is usually broken off in the ground. The roots 

 of winter wheat extend downward seven feet, and the roots 

 of certain trees in arid countries have been known to reach a 

 depth of sixty feet. All the roots of a full-grown corn plant, 

 if cut off and pieced end to end, would reach over one thou- 

 sand feet, and a large squash vine has several miles of roots. 



298. Functions of Roots. Near the ends of the roots 

 are delicate root hairs, which are really cells with very thin 

 walls. They look like a fine fuzz and are estimated to be 

 about 3--J-0- of an inch in diameter. Small as they are, the 



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