16 ELEMENTARY ORGANS OF PLANTS. 



3. The cells, tubes, and fibres, thus associatocl, constitute 

 what botanists call the cellular, vascular, and woody tissues of 

 plants. The first is of universal occurrence; the other two 

 kinds of tissue are only partially introduced or wholly absent 

 from the structure of a great many plants, such as mosses and 

 seaweed, which consist of cellular tissue alone. 



4. That all the parts of plants are fabricated out of cells is 

 evident from the fact that the cellular nature of the vegetable 

 substance ini-ariahly manifests itself when sections of that 

 substance are examined by means of transmitted light under 

 the microscope; the growth or extension of the parts of plants 

 must therefore be the result of the development of new cells, 

 and the size and form of plants must depend on the number 

 and nature of the arrangement of the new cells thus developed. 

 It is therefore proper to begin these investigations by first 

 considering the cells or simple elementary organs of plants 

 separately, and their mode of development into the different 

 tissues; we may then study more profitably the tissues as com- 

 bined together in the form of root, stem, and leaves, which 

 have been very properly termed the compound organs of 

 plants. We shall first show that all the different forms of 

 tissue are only modifications of the cellular, and that they all 

 originate in the simple cell as a point of departure. 



