6 THE PLANT CELL 



part becomes thread-like and seems to assist in the translocation 

 of the chromosotnes (the definite parts into which the nuclear 

 substance becomes segmented during nuclear and cell division) 

 to the opposite pole of the cell; this process may, therefore, be 

 classed as one of the functions of the cytoplasm (see Fig. 3). 



Throughout the life of the cell the cytoplasm has many things 

 to do of a chemical nature, but it is very improbable that it often 

 works independently of the nucleus. Where storage of pro- 

 teids and oils is taking place, we find them stowed away in the 

 meshes of the cytoplasm, and this is good circumstantial evidence 

 that the cytoplasm has manufactured them where we find them. 

 This is particularly true of the insoluble proteids. The cyto- 

 plasm probably secretes the ferments by means of which the 

 stored materials are digested when they are wanted for food. 

 Many other of the ceaseless activities of the cell are doubtless 

 accomplished with its assistance. 



The Nucleus. — In young cells the nucleus is spherical in 

 form and lies at the center imbedded in the cytoplasm and occu- 

 pies from .5 to .8 the diameter of the cell. It consists of the 

 nuclear membrane, nuclear reticulum and nuclear sap, and 

 usually contains one or more nucleoli (Fig. i, A, b). The nuclear 

 membrane appears to be really a part of the cytoplasm, similar 

 to the plasmatic membranes lining the exterior of the cell and of 

 the vacuoles. The reticulum is the essential living part of the 

 nucleus. The nuclear sap appears to be a fluid which fur- 

 nishes to the reticulum water and food and in other ways serves 

 it; while the nucleolus seems to be reserve food of a peculiar 

 kind needed to help in the processes of nuclear and cell division. 



The nucleus is often spoken of as the center of life of the 

 cell. While the statement is vague, it conveys a meaning not 

 entirely misleading. Some of the facts at the foundation of 

 this conception are these: (a) When a protoplast is segmented 

 into two parts by plasmolysis or other artificial means the part 

 containing the nucleus has the power to construct a wall about 

 itself, while the enucleated part has not. Although the plas- 

 matic membrane is the immediate agent in the construction of 



