^9 



^ '^v 



mv: 



H / 





Figure 4-7. Electron Micrograph of Early Telophase Cell from Onion 

 Root Tip. Membrane elements of the endoplasmic reticulum at this stage of 

 cell division appear to orient themselves along the surfaces of the chromo- 

 somes to form the nuclear envelope. The envelope is almost complete in this 

 cell, with the exception of the discontinuity shown in lower half of figure. 

 Note that fragments of membrane elements of the endoplasmic reticulum and 

 small vesicles measuring some 20 m« in diameter have become enclosed, 

 along with the chromosomes, by the nuclear envelope. Polar organization of 

 elements of the endoplasmic reticulum is shown in upper middle of figure. 

 Across the lower margin of the figure numerous phragmosomes are seen in 

 close association with the forming cell plate. (From Porter, K. R. and 

 Machado, R. D., 1960. "Studies on the Endoplasmic Reticulum. IV. Its Form 

 and Distribution During Mitosis in Cells of Onion Root Tip," /. Biophys. 

 Biochem. CytoL, 7, Fig. 15, Plate 93. Courtesy of Dr. Keith R. Porter, The 

 Rockefeller Institute.) 



80 / CHAPTER 4 



