FOUNDATION OF THE CELL THEORY 109 



the amoeboid movements of Mycetozoa. The stream 

 of research was now directed to the discovery of the 

 structure and constitution of protoplasm. After the 

 recognition of the identity of the sarcode of the animal 

 with the protoplasm of the plant, and after the adoption 

 of the name " protoplasm " for both substances, botanists 

 had the invaluable assistance of their colleagues in the 

 sister science in unravelling the problems concerned with 

 it that suggested themselves for solution. 



Another most important question that occupied the 

 minds of biologists at this period was the mode of origin 

 of the varied structural units composing the plant and 

 animal body. Research on this subject was undertaken 

 both by zoologists and botanists, with the result that 

 Schwann, on the animal side, and Schleiden, on the 

 plant side, formulated independently a theory, that all 

 the tissue elements, no matter what were their ultimate 

 forms and functions, were derived from primary isodia- 

 metric cells, and that every cell arose from a pre-existing 

 cell and in the long run from the fertilised ovum. 



The mention of Schleiden's name in relation to the 

 foundation of the cell theory recalls another great service 

 that this distinguished botanist rendered to his science. 

 Previous to 1840 the botanical student had no general 

 textbooks to refer to save the Theorie, elementaire de la 

 botanique and the Physiologic vegetate of De Candolle. 

 These and other treatises were replaced by the famous 

 Grundzuge der wissenschaftlichen Botanik of Schleiden, 

 published in 1842, and translated into English by 

 Lankester, in 1849, under the title, Principles of Scientific 

 Botany, or Botany as an Inductive Science. After an 

 Introduction dealing with general principles, Schleiden 

 devotes his first " Book " to an account of the inorganic 

 and organic constituents of plants. The second " Book " 

 treats of plant cells and tissues and their functions, while 

 in the third he discusses the general and special mor- 

 phology of plants. The fourth " Book " deals with 



