INTRODUCTION 



xv 



cells with unevenly but heavily-thickened walls. The walls are soft 

 extensible and rich in cellulose and pectin. Collenchyma cells may 

 be recognized by their wall pattern. 





O 





B© 



Fig. 1. Cell and wall variations in plant tissues. A, thick-walled 

 Pith; B, collenchyma; C, sclerenchyma, showing sclereids and parenchyma 

 cells; D, tracheid; E, libriform fibre; F, vessel element; G, sieve cell with 

 companion cell. (From Eames, A. J. and Mac Daniels, L. H., An Intro- 

 duction to Plant Anatomy, 2nd ed., pp. 83-96. McGraw-Hill, New York, 



1947.) 



