CHAPTER IV 



THE ANATOMY AND PHYSIOLOGY OF PLANTS 



PLANTS of all kinds make their growth by multi- 

 plication of minute box-like forms called cells. In 

 the lowest forms of plant life the entire plant con- 

 sists of a single cell containing the living matter known 

 to botanists as protoplasm. This living matter, though 

 itself a formless substance resembling the white of an egg, 

 does all the work of the plant. From material carried by 

 this formless protoplasm it builds the walls of its cell and 

 carries on all the functions of life. As plants develop in 

 complexity we find that the first increase of these cells is 

 in long strings, cell added to cell in straight rows. With 

 little higher organism, as in mosses, they are formed into 

 flat tissues by the union of these rows of cells, making 

 some resemblance to the true leaves of the higher plants. 

 When we come to the ferns we find a greater complexity, 

 certain cells taking on certain work and others making 

 quite different forms. Then in our ordinary forest trees 

 we find a still greater complexity and division of labor 

 between the various cells. 



By examining the cross-section of one of our trees we 

 can see with the naked eye a series of rings of growth 

 around a common center. Examining these rings with a 

 microscope we find that the appearance of rings is pro- 

 duced by the decrease in the size of the cells and the thick- 

 ening of their walls toward the close of the season, the new 



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