CHAPTER VI 



Wall Structure in Thick Cell Walls. The Green Algae 



Introduction 



WE NOW turn to the main purpose of this book — a consideration of 

 the wall organization in plant cells in terms of the submicro- 

 scopic structure of cellulose. Whichever of the two aspects are tem- 

 porarily adopted from which wall studies may be regarded (p. 2), 

 and even if interest is confined to commercial matters, the information 

 required is precisely the same. Perhaps we may note at the outset what 

 these desiderata may be. They may be listed as follows: 



(1) The molecular chains of cellulose usually lie along some particular 

 direction in the cell. It is necessary to define this direction in terms of 

 some recognizable morphological axis of the cell. Different layers in a 

 wall often have different directions, when it becomes necessary to 

 define the direction in each and every layer. 



(2) Consideration can then be given to the run of the cellulose chains 

 over the whole cell. 



(3) With one possible exception (p. 81) cellulose is organized into 

 micelles in the sense used here, and it is the average run of the micelles 

 which is involved in (1) above. Since the micelles never do lie parallel to 

 each other in any strict sense it is desirable, sometimes imperative, to 

 know something about the "scatter" of the individual micelles about the 

 common "preferred" direction, i.e. to know the angular dispersion. 



(4) "Micelle breadth" can, and does vary widely and this may have a 

 very considerable effect on the properties of a wall. It is desirable there- 

 fore to have some estimate of micelle dimensions. In view of the state- 

 ments made earlier it should be clear that nothing can be said about 

 micelle length; a more fundamental determination would be that of 

 chain length, but the chains found in untreated walls are so long that 

 variations such as occur are not expected to have any appreciable 

 effect. 



(5) Similarly the intermicellar "spaces" may occasionally diverge 

 widely from the normal and in these cases it is desirable to have some 

 measure of this divergence. 



(6) Finally, and associated closely with (4) and (5), it is profitable to 



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