12 



NATURE OF CELLS 



Tr'-^-sp. 



—TV- 



every vitally active plant and animal cell, this granular 

 liquid protoplasm is found. It is the essence of hfe and is 



a wonderful substance. It 

 makes new flesh, blood, and 

 bone. In fact, protoplasm 

 does everything that is ac- 

 complished in an animal or 

 plant. 



In a living cell, the proto- 

 plasm is not of the same 

 structure throughout ; some 

 parts of it differing greatly 

 in structure and function 

 from other parts. For ex- 

 ample, a small, well-defined 

 spot may be seen, usually 

 along one side of the cell of 

 the melon hair, about mid- 

 way of its length. This is 

 an organized structure of the 

 protoplasm known as the 

 nucleus. The remainder of 

 the protoplasm in the cell 

 is much thinner than the 

 nucleus, has a different func- 

 tion to perform, and is 



The 



streams of protoplasm ; n, nucleus. 



to run toward the nucleus or 

 away from it. In other words they all seem to begin and 

 end there. Even without other evidence this would show 

 that the nucleus must be very important. It is plain that 



m^'iM 





A 



Fig. 3.— A, hair of melon vine, show- knoWU aS CVtoplasm. 

 ing cells ; B, cell much enlarged ;sp, <■ 



streams of cytoplasm seem 



