CONSTITUTION AND ARCHITECTURE IN THE CELL WALL 3 



(1) Non-cellulosic polysaccharides. 



(2) Pectic substances. 



(3) Polyuronide hemicelluloses. 



(4) Lignin. 



In addition, cuticular substances, mucilages, tannins, pigments, 

 and terpenoid compounds are present in various amounts. 



It is not possible to obtain clear separation and maximum 

 recovery of each of the major components by means of a single 

 fractionation scheme. Hence, some isolation procedures must be 

 designed for quantitative recovery of one or a few components 

 in essentially pure form at the sacrifice of other constituents, which 

 must, then, be approached by other techniques. 



Fractionation procedures may sometimes be facilitated by 

 enzyme treatments. Thus, the pectic enzymes may be used for 

 removal of the various pectic compounds, and cellulase can be 

 applied for dissolution of cellulose. Such procedures are most 

 useful as pretreatments to render other components, especially 

 lignin, more accessible to milder solvent extractions. More general- 

 ized microbial attack upon cell wall materials may lead to removal 

 of all but the most resistant substances such as lignins and cuti- 

 cular materials. 



After the cell wall components have been separated and reco- 

 vered in purified form, they may be identified and analyzed. 



Cellulose is commonly identified as a residual substance after 

 removal of other wall components by successive chlorine-Na 2 S0 3 

 and alkali treatment. This virtually pure residue may be further 

 analyzed for contaminants and ash, or may be dissolved in cupram- 

 monium, reprecipitated by acid, and weighed as purified cellulose. 



The non-cellulosic polysaccharides include a variety of carbo- 

 hydrate polymers whose specific analytical properties differ. Col- 

 lectively, they may be determined, however, after treatment of the 

 whole cell wall with chlorine combined with Na 2 S0 3 or ethanol- 

 amine as the fraction soluble in cold 17.5 per cent NaOH. 



The pectic substances are determined after removal of poly- 

 uronide hemicelluloses with cold 4 per cent NaOH, by solubiliza- 

 tion in 0.05 N HC1, alkaline hydrolysis, and alcohol precipitation 

 as calcium pectate. Residual pectic substances which sometimes 



