20 GENERAL BIOLOGY 



reveal, but there are certain structures that are 

 common to all cells, and they may be considered 

 fundamental in cell organization. Postponing for 

 a moment the consideration of the outer limit of the 



FIG. 4. Diagram of a composite cell. M, metaplasmic bodies; v, 

 vacuoles ; pi, plastids (chloroplasts) ; c, attraction sphere inclosing a 

 double centrosome ; nu, true nucleolus ; chr, chromatin network ; /, linin 

 network ; k, karyosome or chromatin nucleolus. Vacuoles are especially 

 characteristic of plant cells. The chloroplasts are found only in plant 

 cells'. They are capable of independent growth and reproduction. It is 

 these that give the green color to leaves. (From Wilson.) 



cell or cell-wall, we find that all cells agree in having 

 the protoplasm composing them differentiated into 

 two parts, a more or less central one, the nucleus, 

 often rounded in outline and somewhat dense in con- 

 sistency, which is surrounded by a less dense area, 



