THE STRUCTURE OF ECONOMIC PLANTS 



The terminology used with reference to the constituent parts 

 of the cell wall has been confusing and contradictory, but Kerr and 

 Bailey (^5) have proposed a system of nomenclature with which 

 Frey-Wyssling (19), Anderson (i), and others working on cell 

 structure are in general agreement. Briefly summarized, they 

 suggest that the term primary wall "should no longer be applied to 

 the first formed layer of secondary thickening, but should be used 



solely in designating the cambial 

 wall and its homologues in other 

 tissues." With reference to the 

 term middle lamella, they suggest 

 that "it should be used synony- 

 mously with intercellular substance 

 in referring to the truly isotropic 

 layer of intercellular material." 

 These recommendations are based 

 upon investigations which indi- 

 cate that cambial initials have 

 walls that are independent mor- 

 phological structures composed 

 chiefly of cellulose and pectic sub- 

 stances and that they are aniso- 

 tropic; while the intercellular 

 substance (middle lamella) be- 

 tween the walls of adjacent 



Fig. 1. A, diagrammatic transection of initials is an amorphouS, isO- 

 one entire tracheid and parts of seven others; . n • i j i i 



B, section of adjacent walls more highly trOplC COlloid, COmpOSed largely 



magnified: a, truly isotropic intercellular of pCCtic SubstanceS deposited by 

 substance; b, cambial or primary wall; c, , ^„. . „ -^ 



outer layer of secondary wall; d, central the CytOplasm. (^hlg. X, A, D.J 



layer of secondary wall; e, inner layer of An important characteristic of 

 secondary wail. (Redrawn from Kerr and , . n i „ „ ,u^^^^^^ '.c ;<-c 



Bailey, Jour. Arnold Arb.) ^he intercellular substance is Its 



plasticity, which permits the 

 intercellular movements and adjustments that are necessary in the 

 development of cambial or meristematic derivatives. 



Recently, Bailey (4) has reemphasized the necessity of critical 

 cell wall analysis, stating that "in any discussion of the higher 

 plants, it is essential to differentiate accurately and consistently 

 between three distinct categories of structures." These are: 

 (i) the meristematic, embryonic, or cambial cells and derivatives of 

 them which have retained their capacity for growth and increase in 



