148 KEITH R. PORTER 



During anaphase of mitosis, lamellar and tubular elements of the ER, 

 now divided between the two ends of the cell, invade the spindle from the 

 poles and sides and approach, from opposite directions, the equator of the 



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10 



Fk;. 10. Micrograph showing di\ rIuil; clII in cortex ot onion root tip. Telophase 

 nuclei are indicated at A'^, cell plate at cp, and surrounding walls at cw. Numerous 

 slender profiles of the endoplasmic reticulum (er) are scattered throughout the 

 cytoplasm. At the level of the plate, and especially at its margins (arrows), the ER 

 profiles are much shorter and describe the existence here of a compact, irregular 

 lattice of tubular elements. Within this there appear first the small pectin vesicles 

 which by their growth and fusion achieve the separation of the daughter cells. At 

 the centre of the plate (cp) this has already happened, but at the margins, the cells 

 are still not divided. 



spindle. As they reach this level, they reticulate very much as they do at 

 the cell surface (Fig. 9). There results from this a tri-dimensional inter- 

 mingling of tubular elements from the two daughter protoplasts and it is 



