30 STRUCTURAL BOTANY 



this substance is the primary part of the cell, while 

 the cell-wall is a secondary product derived from it. 



Embedded in the protoplasm is a roundish denser 

 body, which has a more coarsely granular appearance 

 than the protoplasm itself. This body is the nucleus. 

 A nucleus is certainly present in all living cells of the 

 higher plants, and possibly in all cells whatsoever. In 



FIG. 14 Young cells at various stages of growth. A, Very 

 early stage; the cell -walls are quite thin, and the 

 protoplasm almost fills the cell. , Rather older cell, 

 cell -wall thicker, and vacuoles more numerous. C, Older 

 still ; the greater part of the cavity now forms a large 

 vacuole. n, nucleus ; , vacnoles. (Alter Van Tieghem.) 

 Magnified several hundred times. 



very young cells it is of relatively large size, and its 

 diameter may be more than half that of the entire 

 cell. Its complicated structure cannot be fully de- 

 scribed here, but it may be mentioned that in many 

 cases the apparent granules are found, under a 



