CHAPTER I 



THE CELL 



Cytology, or the study of the cell, has taken its place 

 among the sciences almost entirely since i860. Prior to 

 that date the cell theory of Schwann and Schleiden had 

 been formulated, and its importance was becoming more 

 and more recognized each year. So far as plants were 

 concerned, however, the theory was only partially realized ; 

 and the dominance of the protoplasm in the cell had still 

 to be discovered. Many writers of the time apparently 

 had little idea of its importance, for they included it with 

 many other substances under the general term of ' cell- 

 contents '. The cell wall was looked upon as the visible 

 representation of the cell, instead of as a very subordinate 

 part of its organization. 



The cell theory was extended in its application and its 

 importance as bearing on the development of the current 

 views on embryology and evolution greatly promoted by 

 the researches (among others) of Hertwig, Strasburger, and 

 Van Beneden from 1873 onwards. Of particular conse- 

 quence was the identification of the cell-nucleus as directly 

 concerned in inheritance, made by these writers and Weis- 

 mann some ten years later. 



During the progress of this research, however, the 

 point of view was wholly changed by the recognition 

 that the living substance of animal and plant is of simi- 

 lar nature, if not absolutely identical. The researches 

 of Max Schulze, especially between 1854 and 1863, con- 

 tributed very materially to this result. He was the first 

 to prove that the ' protoplasm ' of von Mohl, studied 



