Nuclear bou ndory 



Chromocenter 



Nucleoplasm 

 Chromosome 



Figure 4-1. Schematic Representation of the Interphase Nucleus. Note as- 

 sociation of parts of the chromosomes with the nuclear boundary and 

 nucleolus. 



Nuclear Envelope 

 There is considerable question as to whether or not the nuclear 

 envelope is actually a semipermeable structure. The available evidence 

 relating to its permeable properties does not preclude the passage 



f 



0.2/t 



Figure 4-2. Electron Micrograph of Section of Nuclear Envelope of 

 Macronucleus of Poramecium multimicromicleatum. The nuclear envelope 

 is a double structure formed by two membranes spaced apart by about 300 A 

 and surrounding the contents of the nucleus. Between the membranes is the 

 perinuclear space. At points indicated by arrows, pores are formed where 

 the inner and outer membranes of the envelope are joined with one another. 

 (From Watson, M. L., 1955. "The Nuclear Envelope. Its Structure and 

 Relation to Cytoplasmic Membranes," J. Biophys. Biochem. CytoL, 1, Fig. 3, 

 Plate 71.) 



STRUCTURE AND FUNCTION OF THE NUCLEUS / 75 



