56 GENERAL BOTANY 



latter idea was first formally established and published by 

 Max Schultze in 1863. This essential identity in cellular 

 structure, and in the nature of the living substance of all 

 organisms, explains the great similarity which has long been 

 known to exist between the lowest plants and animals. Indeed, 

 this similarity is so great that certain organisms are to-day 

 claimed by botanists as belonging to the plant kingdom and by 

 zoologists as belonging to the animal kingdom. The great 

 importance of the cell theory can only be realized by the stu- 

 dent as we proceed to study more intimately the biology of the 

 higher and the lower plants, in which we find exactly the same 

 processes performed by very different structures and organs of the 

 plant body. 



LATER DISCOVERIES AND THEORIES 



The later developments of the cell theory were the result 

 of researches and discoveries made by a notable group of 

 biologists during the latter part of the nineteenth century. 

 These later observers applied the early ideas and discoveries 

 concerning the structure of the cell and protoplasm to prob- 

 lems concerned with the ultimate structure of protoplasm and 

 nucleus, cell divisions, fertilization, and development, and to 

 the fundamental processes of plant and animal physiology. 

 Their discoveries and conclusions in these various fields can 

 only be outlined here, but the following brief survey is given in 

 order that the student may realize, in part at least, the full 

 significance of the cell theory to modern biological thought 

 and discovery. 



Cell division. The general process of cell division in the 

 higher plants was first correctly interpreted by Karl Nageli 

 in 1846, although Schleiden and Von Mohl made large con- 

 tributions to the final solution of the problem. 



Basing their observations on those of Nageli, Von Mohl, and 

 Schleiden, the later botanists of the nineteenth century, under 

 the leadership of Eduard Strasburger, the great German botanist, 

 worked out in much greater detail the mechanism and the mean- 

 ing of the division process now designated as mitosis. 



