various elements of the endoplasmic reticulum have been interpreted as 

 indicating either that the nuclear envelope is a modification of the cyto- 

 plasmic membrane system or that certain membrane components of the 



Figure 4-5. Electron Micrograph of Portion of a Meristematic Rootcap Cell 

 of Maize, Showing a Double-layered Nuclear Envelope with Distinct Pores. 

 Note continuity of the outer membrane of the nuclear envelope with double 

 membrane element of the endoplasmic reticulum. Mitochondria, a Golgi 

 apparatus (lower left in figure), and unidentified cytoplasmic inclusions are 

 shown. (From Whaley. W. G., Mollenhauer. H. H.. and Leech, J. H., I960. 

 ■'The Ultrastructure of the Meristematic Cell." Am. J. Botany, 47, Fig. 3, 

 p. 425. Courtesy of Dr. W. Gordon Whaley. University of Texas.) 



cytoplasm are of nuclear origin. The observations made on the ultra- 

 structure of the nuclear envelope indicate a complex structural organiza- 

 tion which may correspond to regions of different permeable properties. 



78 / CHAPTER 4 



