42 PLANT GROWTH SUBSTANCES 



causing considerable financial loss. The softening of pickles is associated 

 with a decrease in the chain length of the pectic molecules (i). Con- 

 versely, it is well known that calcium salts harden the texture of pickled 

 vegetables presumably by forming calcium pectate with cross linkages. 



Considering all the properties of pectic substances, the property of 

 the primary wall could be explained if it were assumed that the pectic 

 substances were the continuous phase of the wall and the cellulose micro- 

 fibrils were a discontinuous phase. The cellulose fibrils might be con- 

 sidered as structural reinforcement. Changes that occur during growth 

 would affect the easily hydrolyzable pectic substances and not the 

 cellulose. Changes in elastic extension of the wall could be explained as 

 changes in hydration of the pectic gel. This hypothesis has not been 

 proved but it has been brought forward to get around the impasse that 

 the properties of the primary membrane are not the properties of a 

 sheet of cellulose. 



The primary wall has been pictured as a fibrillar network of cellulose. 

 A wall built in this manner would not have the elastic extensibility 

 characteristics of primary membranes. Considering the properties of 

 cellulose and pectic substances, the properties of the primary wall can 

 be explained if it is assumed that the protopectin forms a continuous 

 phase and the cellulose microfibrils form a discontinuous phase. 



REFERENCES 



1. Bell, T. A. and Etchells, J. L., Food Technology (In Press). 



2. Berkley, E. E., Textile Res., 9:355-375 (1939)- 



3. , and Kerr, T., Ind. and Eng. Chem., 38:304-309 (1946). 



4. Bonner, ]., Jahrb.f. wiss. Bot., 82:377 (1935). 



5. Frey-Wyssling, a., Growth Symposium, 12:151-169 (1948). 



6. Hessler, L. E., Merola, G. V., and Berkley, E. E., Textile Res., 



18:628-634 (1948). 



7. Heyn, a. N. S., Botan. Rev., 6:515-574 (1940). 



8. JosLYN, M. A. and Phaff, H. J., Wallerstein Lab. Communication 



10:39-56 (1947). 



9. MuHLETHALER, K., Btochem et Biophys, 3:15-25 (1949). 



10. Owens, H. S., Lotzkar, H., Schultz, T. H., and Maclay, W. D., 



/. Am. Chem. Sac, 68:1628-1632 (1946). 



11. Preston, R. D., "The Organization of the Cell Wall in Plants," in 



Fiber Science (edited by J. M. Preston,The Textile Institute, Manchester, 

 England, 1949). 



