STRUCTURAL FACTORS IN POLYMERIZATION 47 



specifically associated with the cell wall, the pectic substances, polygalacturonic 

 acids of about 20,000 molecular weight, which may exceed cellulose in amount (2) 

 offered a further material for comparison. The pectic acid matrix was approxi- 

 mately loo-fold greater in yield than the cellulose system, and considerably more 

 active than methylcelluloses. It was further noted that gelation of pectic acid 

 with C'a(II) reduced its activity substantially. Recently it has been observed that 

 the region of young wood fiber cells staining with Ruthenium Red corresponded 

 to the region first showing deposits of strongly ultraviolet-absorbing substance 

 (40, 41) and that the intensity of the Ruthenium Red reaction diminishes as 

 lignification proceeds (i). Although this dye may be bound by many polymeric 

 acids, its reaction in young cell walls is limited almost completely to pectic acid 

 (19), whence it may be concluded that the differences observed between cellu- 

 losic and pectic acid matrix systems constituted a reasonable reflection of an 

 actual histophysiological pattern of lignification to be found under natural con- 

 ditions. 



Additional evidence suggesting the importance of pectic substances in lignifica- 

 tion was obtained by treatment of celery vascular strands with a selection of 

 enzymes prior to incubation with eugenol-peroxide solutions. After exposure of 

 tissue to I per cent pectinase (20 hr., 25 °C), all rigidity was lost and lignin forma- 

 tion was reduced to 30 per cent of the control yield. With cellulase, 60—65 P^r 

 cent of the original activity was retained; and with pepsin, only 15-25 per cent of 

 the initial lignifying ability remained. Thus, the native cell wall matrix is primarily 

 susceptible to attack on its protein (peroxidase?) and pectic components, sec- 

 ondarily by disturbance of at least the superficial layers of cellulose. 



Variations on the Biopolymer Matrix. The nature of eugenol, its probable deriv- 

 atives and the polysaccharide matrix emphasize hydrogen bonding as the principal 

 intermolecular force involved in orientation of the lignin monomer. It was there- 

 fore of interest to test as matrices substances somewhat removed from the general 

 polysaccharide type. In the presence of the adsorbents alumina and silica gel, 

 eugenol was not converted into lignin (32), but lignin or lignin-like products 

 were formed in the presence of the minerals amphibole, serpentine and kaolin 

 (table 5). Products formed in the presence of amphibole possessed an absorption 



Table 5. Spectral features of products formed on mineral matrices 



MATRIX 



Amphibole 

 Amphibole 

 Serpentine 

 Kaolin 



As defined by fig. 3. 



