THE ENDOPLASMIC RETICULUM 



H9 



within this lattice that the so-called pectin vesicles appear (Figs. lo and 

 ii). These increase in number and size from the centre of the plate out- 

 wards, and finally fuse to complete the separation of the two cells [45]. It 

 is not possible at this time to account for the origin of the vesicles, but it 

 would seem that small, restricted loci in the spindle matrix are lysed or 

 otherwise changed and enclosed bv a membrane — possiblv bv virtue of this 



^'W^"'"!^' W 



pv 



1 N 



(^ 



ph ^ 



-^ ■ ^ 



er-— 



I 



cw 



11 



Fig. 1 1. This shows, at higher magnifications, the right-hand margin of the cell 

 plate in Fig. 10. The region of the phragmoplast is indicated at ph. Within the 

 lattice of tubules, which marks the phragmoplast and the advancing margin of the 

 plate, the pectin vesicles {pv) first appear. To the left, in this image and toward 

 the centre of the plate, these have already fused. The outer surface and wall of the 

 cell are at cic. 



change. The important thing for present purposes is to note the very 

 intimate association of this ER or ER derivative with the events of plate 

 and new wall formation. Whether the small marginal units of the ER 

 contribute enzyme or substrate to the biochemical events leading to pectin 

 and /or early cellulose formation cannot be decided from evidence available. 

 One may suggest, however, that the results of any participation which the 

 ER may take in plate and primary wall formation should reflect any 

 patterns or irregularities in the distribution of elements in the ER. 



The intimacy shown here between the ER and the cell surface is again 



