PLANT ANATOMY 



CHAPTER I 

 THE PLANT CELL 



The plant body is composed of structural units termed cells. 

 These are minute boxes often barely visible and usually en- 

 tirely indistinguishable to the naked eye. The walls of the 

 boxes are composed of cellulose, wood, or cork, or a substance 

 allied to cork called cutin. As a rule, the walls are without 

 apparent perforations. The term cell has also come to include 

 the living body which is always present in young cells and very 

 frequently in old ones. 



The discovery that the plant body is composed of the cell 

 units was made by Robert Hooke, who, about 1660, with a com- 

 pound microscope improved by himself, saw the cellular struc- 

 ture of cork. The cells of cork have the appearance of the cells 

 of honeycomb, and this similarity led to his use of the word 

 ''cell" for the structural units of the cork, and ultimately to the 

 extension of the usage to plants in general. The term is not 

 an unfortunate one for cells considered merely as boxes; but its 

 application to the living parts inclosed within the cell-walls, or 

 to the living part where no wall is present is inapt. The terin 

 protoplast (Gr. protos, first, and plastos, formed, the thing first 

 formed) is now in general use to designate the living part of the 

 cell as a morphological unit; and the term protoplasm or plasma 

 is applied to the substance composing the protoplast, just as a 

 brick would be a morphological unit of a brick house, and burnt 

 clay the substance composing it. Following the general usage 

 the word cell will here be applied to the box and its living content 



I 



