250 MACROMOLECULAR COMPLEXES 



coarse bands oriented with respect to the cell axis. At some point 

 in the band— which presumably already contains a microfibril end- 

 synthesis begins. As this proceeds, the microfibril end moves for- 

 ward through the coarse band and new parts of the band take over 

 synthesis. At this time, the coarse band has a central core of cellu- 

 lose and an outer sheath of protein— the reverse of the condition in 

 animal skin. It is not clear whether the diameter of the microfibril 

 ( which varies only within rather narrow limits ) is a function of the 

 size of the protein aggregates or is controlled thermodynamicallv as 

 suggested by the work of Fiirth ( 1955 ) . 



Eventually the cellulose-protein complex must disintegrate, so 

 that the microfibril lies free on the wall surface. 



When these protein aggregates take up a new alignment in prep- 

 aration for the deposition of the next lamella, it would then follow 

 that synthesis of the new lamella could begin only at microfibril 

 ends of the lamellae just completed. This would explain the manv 

 interweavings between microfibrils of different lamellae. This does 

 not in any sense "explain" the specific orientations of cellulose micro- 

 fibrils, but merely puts the mechanism one step further back into 

 the cytoplasm. In spite of earlier criticisms of orientation by proto- 

 plasmic streaming, it seems possible that in some plants there is 

 some association between streaming and orientation and that this is 

 achieved through orientation of proteins (Probine and Preston, 

 1958). It is not at the moment possible to decide whether streaming 

 is involved in the cases discussed in this paper. 



These considerations refer specifically, of course, only to those 

 few algae in which microfibrillar orientation is so perfect that the 

 necessary critical observations have been made. It seems unlikely, 

 however, that the basic principles will be different in other plants. 

 The present situation is, in brief, that such evidence as is available 

 points toward the type of mechanism which mav be involved in wall 

 synthesis. Further progress clearly demands a thorough biochemical 

 study of the proteins in or near the cytoplasmic surface. 



References 



Akiya, a., and M. Tomoda. 1956. /. Pharm. Soc. Japan 76: 1092. (Cited in Hall 



et al, 1960.) 

 Allsopp, a., and P. Misra. 1940. The constitution of the cambium, the new wood 



and the mature sapwood of the common ash, the common elm and the Scotch 



pine. Biochem. J. 34: 1078-1084. 



