CHAPTER I 

 THE CELL 



The cell is the unit of the living organism whether plant or 

 animal. That is, all prganis.ms, both plants and animals, are 

 made up of one or more cells. The term cell is generally used 

 to imply a minute box-like structure with walls which may or 

 may not be filled with protoplasm or other substances ; but a liv- 

 ing, organized body of protoplasm may be considered a cell, 

 regardless of the presence or absence of the cell wall. Of course, 

 the empty cells which we see under the microscope were at one 

 time filled with protoplasm. Plant cells vary in diameter 

 from 1/1000 to 1/100 of an inch and can be readily seen in a 

 thin piece of plant material when examined under a microscope. 



Historical. — Of course, our knowledge of the cell began with 

 the invention of the microscope, for it was impossible to see the 

 cell previous to that time. Kobert Hook (1635-1703), an Eng- 

 lishman, was one of the early workers with the microscope and 

 was the first to demonstrate the cell about the year 1660. He 

 studied thin sections of plants and used the term " cell " in 

 describing' the structures which he saw, comparing them with the 

 cells of the honeycomb. Marcello Malpighi (1674) (Fig. 1), an 

 Italian, and ISTehemiah Grew (1682) (Fig. 2), an Englishman, 

 added greatly to our knowledge of plant cells and are frequently 

 called the " fathers of plant anatomy." The microscopes used by 

 these early workers were extremely crude as compared with the 

 highly complex instruments of to-day, and they were unable to 

 recognize anything other tiian the cell walls. 



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