The electron microscope studies published to date on the submicro- 

 scopic structure of the cytoplasm are more or less in general agreement 

 concerning the reality of the endoplasmic reticulum, but considerable 



r' 



Figure 3-24. Electron Micrograph of Portion of Cytoplasm of Rat 

 Parenchymal Liver Cell. Note local differentiation of membrane elements 

 of the endoplasmic reticulum into smooth- and rough-surfaced types. The 

 smooth-surfaced elements (ss) appear as vesicles and tubules disposed in 

 discontinuous groups mostly at the periphery of the cell. The rough-surfaced 

 elements (rsj rso) are arranged more or less parallel to one another in large 

 arrays. Profiles of rough-surfaced elements sectioned normal to their surface 

 are marked as rsj, and oblique to their surface as rso. Points of continuity 

 between the smooth- and rough-surfaced elements are indicated by arrows. 

 Numerous mitochondria (m) are seen in the field. (From Palade, G. E., 

 1956. "The Endoplasmic Reticulum," J. Biophys. Biochem. CytoL, 2, Suppl., 

 Fig. 3, Plate 33.) 



confusion still exists regarding terminology and interpretation of indi- 

 vidual components of the system. For example, the cisternae are inter- 

 preted by Porter and Palade as pairs of membranes arranged in parallel 

 and connected at their ends. Sjostrand (1956), on the other hand, 

 suggests that the cisternae actually represent a discontinuous series of 



STRUCTURE AND FUNCTION OF CYTOPLASMIC ORGANELLES / 53 



