14 



THE PLANT CELL WALL 



to those who study the physiological chemistry of growth (Table 3). 

 In analyses separated by a quarter century, major differences in 

 all principle wall components exist. The most significant distinction 

 lies in the pectic substances which have been specifically implicated 

 in the hormonal regulation of cell extension. In the older analysis, 

 the pectic substances form an appreciable part of the wall, whereas 

 the more recent analysis demonstrates only trace amounts. It has 

 been claimed that ammonium oxalate solubility, which is commonly 



Table 3. Constitution of the Coleoptilar Cell Wall of Avena 



adduced as evidence for the presence of pectins may be mislead- 

 ing, as polysaccharides other than pectin may also appear in this 

 extractant in appreciable quantities. The significance of this major 

 discrepancy for the interpretation of growth phenomena will be 

 examined further in the discussion of cell wall dynamics, but the 

 warning that it carries should not pass unnoticed. 



Wall Polysaccharides 



On complete acid hydrolysis, cellulose is converted quantita- 

 tively into (3-D-glucose. Controlled hydrolysis yields the disaccharide 

 cellobiose, 4-D-giucopyranose-(3-D-glucopyranoside. Hydrolysis of 

 methylated cellulose yields 2,3,6-trimethylglucose, and no di- 

 methylglucose. Careful anaerobic methylation yields no detectable 

 tetramethylated product. From these facts, cellulose may be 

 pictured as consisting of extremely long, unbranched chains of 

 anhydroglucose residues joined through 1 ,4-linkages. 



The crystallinity of cellulose has been clearly established by 

 X-ray diffraction planes normal to the axis at 10.3 A intervals, 



