30 



THE HISTORY OF CELLS 



celhvdl 

 plccsma 



^nucleus 

 -chloroplost 





a result of the studies of 

 the scientists previously 

 named, the cell theory was 

 further developed. It was 

 now stated that all plants 

 and animals are made of 

 cells and cell products. 

 The cell is the structural 

 and physiological unit of 

 the organism. The living 

 organism can perform cer- 

 tain functions because its 

 cells are adapted to per- 

 form these functions. 

 Other scientists, using this 

 theory as their basis, have 

 been able to show the im- 



Compare the cells of Elodea shown in the diagram with portance of the Cell in the 

 those you studied under the microscope. r l e ' 



development of organisms 



and something of its importance in heredity. Many scientists 

 are still investigating the structure and functions of cells and 

 others are studying the cell in its relation to the development of 

 the organism. This work, in spite of the fact that three centuries 

 have passed, is still in a developmental stage. 



Cellular nature of plants. The cells of green plants are not all 

 alike in size and shape. A narcissus leaf is made of many layers 

 of cells which vary in shape. 



Problem. Study of the epidermis of the narcissus leaf. 



I. Peel off a small strip of the thin lower surface (epidermis) of a narcissus 

 leaf. Mount it for study, and focus it under the microscope. 



A . Describe two different kinds of cells that are seen. 



B. Note the small oval opening between paired cells. Suggest a use 

 for these openings ; for the cells that form them. 



