THE CELL AND THE CELL THEORY 59 



SUMMARY 



1. The cell discovered and named as a unit of organic structure 



in plants (Robert Hooke, 1665). 



2. The nucleus discovered in orchidaceous plants (Robert Brown, 



1831). 



3. The term protoplasm applied to living substance of plant cells 



(Von Mohl, 1846). 



4. Cell theory announced (Schleiden and Schwann, 1839). 



5. Cell division correctly interpreted (Nageli, Von Mohl, and 



Schleiden, about 1846). 



6. Cell differentiation and tissue structure explained (Von Mohl 



and contemporaries, 1840-1850). 



7. Later developments of the cell theory : 



a. Fertilization in Spirogyra (1879) ; in higher plants (Stras- 



burger, 1884). 



b. Development of plant embryo (Hanstein, 1869). 



c. Cytology (1873-1900). Minute structure of cytoplasm 



and nucleus ; details of nuclear and cell division. Stras- 

 burger the leading botanist of this period in cytology. 



d. Physiology of plants (1860-1900). Sachs and Pfeffer the 



most prominent plant physiologists. 



The above summary indicates the general course of the in- 

 vestigations and discoveries which have established the cell 

 theory and have furnished us with our present knowledge of 

 the structure and development of organisms. The student who 

 has followed this development of the cell theory will be better 

 fitted to understand the bearing of the more detailed account 

 of the cell structure, development, and activities of plants which 

 now follows in the text. 



