CONSTITUTION AND ARCHITECTURE IN THE CELL WALL 



13 



the proportions of their constituents (Table 2). Relative to the 

 other major substances, cellulose shows somewhat less variation 

 among the samples given. In contrast, the non-cellulosic poly- 

 saccharides, pectic substances, and polyuronide hemicelluloses vary 

 by as much as seven- to sixty-fold. 



Table 2. Percentage Cell Wall Composition in Various 



Plant Organs 



In spite of these extreme variations in individual non-cellulosic 

 components, their sum has no more range than does cellulose 

 itself. This relationship suggests that in the cell wall the relatively 

 constant cellulose is associated with a relatively constant 

 interstitial aggregate whose composition varies, perhaps in a funct- 

 ional and dynamic fashion. We shall have occasion to return to 

 this proposition later. Analytical data on cell wall substance is of 

 vital importance to an understanding of biosynthetic processes, 

 particularly in cellular growth and differentiation. The serious 

 consideration of detailed analyses is, however, hampered by the 

 coexistence of data obtained over a span of years by the use of 

 fractionation procedures which have themselves been subject 

 to revision and improvement. Rarely has there been opportunity 

 for a critical comparison of older and newer methods for cell wall 

 fractionation. A particularly important comparison does exist, 

 however, for the Avena coleoptile, an organ of critical importance 



