xiv INTRODUCTION 



however, one of the great frontier areas of quantitative biology. 

 The nature of the interactions between the genomes of individual 

 cells and biotic, physical, and chemical components of their environ- 

 ment are largely obscure, although the consequences of such 

 interactions are always in evidence. 



A study of the cell wall in its several aspects provides one 

 approach to problems of cellular differentiation. In the pursuit of 

 this study, consideration must be given to constitutional and 

 architectural features of cell walls; to the material transforma- 

 tions associated with wall substance and the chemical and physical 

 means for their regulation. Although the cell wall of the vascular 

 plant has been selected as a major subject, a proper biological 

 perspective requires comparative treatment of walls and kindred 

 intercellular systems as they exist among organisms at large. 

 Historical perspective is provided by examination of the phylo- 

 genetic aspects of a durable component of the plant wall, lignin. 

 Among organisms, the walls of plant cells, particularly vascular 

 forms, have been studied most extensively. Purely scholarly con- 

 sideration of plant structure and growth have been reinforced 

 greatly by long-standing economic and technological interests 

 in cell wall derivatives. Accordingly some attention must be given 

 to woods, plastics, fibers, and coal. Such considerations become all 

 the more important when it is recognized that cell wall technology 

 is a function of the fundamental chemistry, physics, and geology 

 of these materials. 



Cell Types and Cell Walls in Vascular Plants 



The identity of tissue types depends upon the anatomical 

 characceristics of their component cells. Simple tissues contain 

 but one cell type, complex tissues two or more. 



Parenchyma, sclerenchyma, and collenchyma represent simple 

 tissues, parenchyma is the primitive, unspecialized tissue consisting 

 of isodiametric cells with active protoplasts and relatively thin 

 walls. Parenchyma cells are the principle or sole constituent of 

 meristems, pith, cortex, and other tissues. Collenchyma, which 

 forms simple, homogeneous tissue, consists of irregular, elongate 



