ments of the reticulum which bear the small granules are termed "rough- 

 surfaced" to distinguish them from the smooth-surfaced ones which are 

 not associated with granules. The smooth-surfaced elements predominate 

 in the cytoplasm of such cells as the mature leucocyte and spermatocyte 



cm 





# 



Figure 3-22. Electron Micrograph of Portion of Rat Spermatocyte. The 

 nucleus is seen in the lower left corner of the figure, surrounded by a double- 

 layered nuclear envelope containing numerous pores (arrows). The endo- 

 plasmic reticulum is predominantly of the smooth-surfaced variety, made up 

 of numerous circular (c) and oval (o) profiles, isolated or in rows (r), and 

 a few elongated membrane elements (e). Profiles with dense particles at- 

 tached to the outer membrane surface are relatively rare (rs). Mitochondria 

 (m) and clusters of small, electron-dense particles (p) are present in the 

 cytoplasm. The cell membrane is visible at cm. (From Palade, G. E., 1956. 

 "The Endoplasmic Reticulum," J. Biophys. Biochein. Cytol., 2, Suppl., Fig. 1, 

 Plate 31.) 



(Figure 3-22), while the rough-surfaced elements are characteristic of 

 exocrine cells of the pancreas and plasma cells (Figure 3-23). 



In protein-synthesizing cells in general both types of membranes are 

 represented (Figure 3-24). The smooth elements appear as tightly 

 packed vesicles which form a randomly disposed network usually at the 



STRUCTURE AND FUNCTION OF CYTOPLASMIC ORGANELLES / 51 



