CHAPTER IV 



HISTORICAL SKETCH (THE CELL AND THE CELL THEORY) 

 EARLY DISCOVERIES AND THEORIES 



Cell wall. The first discovery of the cell structure of plants 

 is attributed to Robert Hooke, an Englishman, who, about the 

 year 1665, observed the cellular structure of plant tissue in 

 sections of the wood, bark, and leaves of plants. Hooke was 

 impressed with the fact that such sections, when viewed under 

 a strong microscope, presented the same appearance as the cells 

 of a honeycomb. He therefore applied the term cell to the 

 cavity which he saw inclosed by the conspicuous . cell walls, 

 which form the cell boundary of most plant cells. This appli- 

 cation of the word cell to the cavity, and not to its contents, 

 is now regarded as a misnomer, since we know that the most 

 important part of plant and animal cells is the living substance, 

 protoplasm, which is contained in the cell cavity. Long usage 

 has so firmly established the term, however, that it is still in use, 

 although its meaning is now extended to include, with the cell 

 wall, the substances within the cell cavity, the most important 

 of which is the living protoplasm. 



The protoplasm and nucleus. The observation of the living 

 substance within the cell cavities of plant and animal cells, 

 and the recognition of its true nature and significance, was not 

 understood for fully two centuries after Hooke made his dis- 

 covery of the cellular structure of plants. This was due in 

 part to faulty observations and in part to the imperfect 

 microscopes with which the observations were made. 



Robert Brown (1831), an English botanist, discovered a 

 dark central body within the cells of orchids, which he named 

 the cell nucleus. Other observers of cellular structure saw a 

 substance outside of the cell nucleus in plant cells, which 



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