68 The Microscope. 



Thus we have seen how the cell and its various parts were 

 gradually discovered, and at the close of this epoch, the cell 

 could be defined as "A vesicle surrounded by a solid membrane^ 

 containing a fluid in which floats a nucleus provided with a. 

 nucleolus, and in which may be seen bodies of various forms." 



II. CELLS AS INDEPENDENT INDIVIDUALITIES. 



At the present day, many naturalists regard the cell as an in- 

 dependant individuality, a sort of elementary organism. This 

 notion finds expression for the first time in the work of Turpin,. 

 as may be seen even on his title-page : " Observations on Every 

 Vesicle Composing Cellular Tissue, Considered as so Many Dis- 

 tinct Individualities, Having their Special Vital Centre of Vegeta- 

 tion and Propagation, and Destined to Form, by Agglomeration^ 

 Compound Individualities in all those Vegetables in which the 

 Organization of the Mass Implies more than one Vesicle." 



Mirbel and Schleiden express themselves no less explicitly. 

 The former says : " Cells are so many living individuals, en- 

 dowed within certain limits, with the properties of growth, 

 multiplication and modification. . . A plant, therefore, is a 

 collective being; " and Schleiden admits that " the cell is a small 

 organism," that " every plant, even the highest, is but an aggre- 

 gate of cells completely individualized and distinct in their 

 existence." Schwann and Hseckel also accept this idea, but 

 others, as Julius Sachs, reject it. This subject will be treated 

 hereafter at greater length. 



III. CELLULAR THEORY. 



Whilst studying the parts of the cell, the scientists were 

 obliged to look for examples among organized bodies ; they could 

 therefore scarcely avoid the studying also of the internal structure 

 of plants and animals. Thus Malpighi, Grew and Leeuwenhoek, 

 relying on their researches and observations, afiirm with the 

 greatest confidence, that the body of a plant is entirely formed 

 of cells in juxtaposition, and the researches of Brisseau Mirbel, 

 of Meyen, of Schleiden, and especially the important memoirs 

 of Hugo von Mohl, published since 1827, completely confirm 

 this statement of Malpighi, Grew and Leeuwenhoek, and at the 

 same time prove that all vegetable tissues, no matter how much 

 they may have become differentiated, are exclusively formed 

 from cells, which are derived one from another, and which have 

 the same genetic origin, although they may have undergone a 



