

Chapter Four ^* ^^ 



CELL STRUCTURE AND PROTOPLASM 



The unit of life is the cell, and one or more of these units 

 constitute the structure of plants and animals. 



Although widely varied in size and shape, most cells are 

 microscopic, somewhat elongated and box-like in structure, 

 with each of their several sides attached to another cell some- 

 what in the fashion of the cells of a honey-comb. The cells 

 in most tissues are so small that in cross section one hundred 

 to one thousand are found per linear inch or ten thousand 

 to more than a million per square inch. Most of them fit 

 together in a definitely organized pattern that gives great 

 strength to a tissue while in some tissues of the plant large 

 cavities occur between and at the corners of the cells. The 

 complexity of the plant is the result of the many parts and of 

 the many different cells of which it is made. The actual 

 number of cells in a bean, petunia or grass plant is not so 

 important if we remember they are so numerous that they 

 have never been counted, but the various kinds have been 

 very well studied and described. It has been said that the 

 surface of the leaf has more than a million radial cell walls 

 per square inch to support it. If we look at a leaf with a 

 mental picture of its cellular structure as shown in the dia- 

 grammatic view of the cells (Fig. 15), highly magnified, we 

 get an idea of the nature of the cell arrangement; those in 

 the blade at the right have large cavities between them while 

 those at the left in the midrib fit closely. Further descrip- 

 tions of cell arrangement and size will be found in the chap- 

 ters on the root and stem, but the details of individual cells 

 are too small to be shown here. 



As shown in the resting stage of Figure 6, a cell has three 

 distinct parts: the cell wall, the protoplasm, and the non- 

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