CONSTITUTION AND ARCHITECTURE IN THE CELL WALL 5 



reaction solvents do not yield a native product, but they are 

 useful in the study of lignin structure. 



After comparatively pure substances have been isolated from 

 the cell wall, their constitution may be examined. The polymeric 

 nature of the major wall components has long been recognized 

 even if their study has only recently been undertaken from the 

 viewpoint of polymer chemistry. In polysaccharide chemistry, one 

 of the foremost analytical procedures is hydrolysis. Acid hydro- 

 lysis degrades polysaccharides, yielding mixtures of lower poly- 

 saccharides, oligosaccharides, and simpler units. Ultimately, the 

 most stable structural units, the monosaccharides may be obtained, 

 but it is also of value to carry out controlled hydrolyses in the 

 hope that relatively stable intermediates, disaccharides for example, 

 may be identified. 



Constituent monosaccharides may of course be identified by 

 means of a variety of chemical and physical properties including 

 optical activity, melting points and crystallographic features of 

 derivatives (osazones formed with phenylhydrazine, for example), 

 titrable acid groups when present, etc. The application of various 

 analytical procedures may be complicated when two or more 

 constituent units are present in the hydrolysate. Specific tests 

 may sometimes suffice to demonstrate the presence of more than 

 one carbohydrate but recourse to separation procedures is also 

 necessary. To the more classical methods of separation based 

 upon physical differences (solubility, for example) among sugars 

 or their derivatives, the techniques of paper and column chromato- 

 graphy may be added. 



The polyfunctioned nature of the sugars allows the existence 

 of a variety of combinations in polysaccharides. The most important 

 variables are made manifest by consideration of a single mono- 

 saccharide unit in the polymer. Thus, we must determine: (a) The 

 number of units linked to a specific residue (linear vs. branched); 

 (b) the frequency of end residues (which contain one more hydroxyl 

 than an internal residue); (c) and the mode of linkage to adjacent 

 residues (which includes both the distinction between a- and 

 ^-isomers and the alcoholic carbon atoms through which linkages 

 are established). 



