THE ENDOPLASMIC RETICULUM 



145 



Fig. 7. This shows the corners of two contiguous meristematic cells of the 

 onion root tip. The primary wall (czv) separating the cells passes across the lower right 

 corner; the nucleus of one cell is at N. The wav'y lines in the cytoplasm are 

 actually paired lines or membranes with an intervening space (see Figs. 11 and 12 

 for higher magnification of same). They represent sections through large lamellar 

 units of the ER. Where these approach closely to the cell surface they branch and 

 reticulate to give in section only small circular profiles (see long surfaces indicated 

 by arrows). Figure 8 shows the appearance of this when section coincides with 

 plane of wall. Other components include mitochondria (m), proplastids (pp), and 

 dictyosomes (d). 



The specimen, from an onion root tip, was fixed in KMn04, embedded in nietha- 

 crylate, and sectioned with a diamond knife. 



