CELLULOSE-PROTEIN COMPLEXES 249 



to project from one end. One example of this, marked by an arrow, 

 is visible in Fig. 14. 



When similar preparations are made of the innermost lamellae 

 of cells which have previouslv been plasmolvzed, these oriented 

 cytoplasmic aggregates remain attached to the lamella. They are 

 therefore more closely attached to the wall than is the bulk of the 

 cytoplasm, which retracts on plasmolysis. A new wall lamella does 

 not develop under these conditions, presumablv because of the with- 

 drawal of the supply of raw materials necessary. The new cytoplas- 

 mic surface does produce a new cell wall, but the microfibrils are 

 not oriented. When, however, filaments plasmolyzed in, say, 0.8M 

 sucrose are returned to sea water, they continue to grow normally. 

 After a few days in sea water, wall layers similar to that illustrated 

 in Fig. 14 can be found deep in the wall, covered by more recent 

 wall lamellae with the usual alternations in microfibril orientation. 

 A cytoplasmic surface, withdrawn from the wall and at that time 

 producing microfibrils oriented at random, can thus reconstitute the 

 whole orientation mechanism. 



Discussion and Conclusions 



Although, so far as the writer is aware, there is no direct bio- 

 chemical evidence of close association between cellulose and pro- 

 tein in plant cell walls, the morphological observations and struc- 

 tural determinations referred to above, together with the evidence 

 from parallel conditions in animals, however, is strongly suggestive. 

 It would appear to be established that microfibrils are synthesized 

 by what appears to be end-synthesis and that, at least during and 

 immediately after synthesis, the part of the microfibril concerned is 

 embedded in an aggregate of granules which may be enzyme com- 

 plexes and therefore largely protein. Microfibrils are occasionally ob- 

 served, on the surface of new wall lamellae, which have long taper- 

 ing ends running down to the limits of visibility in the electron 

 microscope. It would seem, therefore, possible that synthesis occurs 

 over long lengths of microfibril and is end-synthesis of individual 

 molecular chains rather than of whole microfibrils. 



It would certainly be premature to attempt to give even a purely 

 morphological picture of the cellulose-protein complex during syn- 

 thesis. Appearances do suggest, however, that a cytoplasmic surface 

 which is to produce a wall lamella first becomes organized into 



