62 SUBCELLULAR PARTICLES 



28. SiEGEL, S. M. Physiol. Plant. 7: 41, 1954. 



29. SiEGEL, S. M. Physiol. Plant. 8: 20, 1955. 



30. SiEGEL, S. M. Quart. Rcr. Biol. 31: i, 1956. 



31. SiEGEL, S. M. Unpublished observations. 



32. SiEGEL, S. M. /. .!ni. Cheni. Soc. 78: 1753, 1956. 



33. SiEGEL, S. M. /. ylni. Chem. Soc. 79: 1628, 1957. 



34. SiEGEL, S. M. Proc. Nat. Acad. Sci. 43: 811, 1957. 



35. SiECEL, S. M. Unpiililislictl observations. 



36. SiEGEL, S. M. /. Am. Chem. Soc. In press. 



37. SiEGEL, S. M. AND B. Z. SiEGEL. NatiiiT 1 79 : 421, 1957. 



38. SiEGEL, S. M. AND B. Z. SiEGEL. Nature i8i: 1153, 1958. 



39. SOLBERG, R. AND N. HiGINBOTHAM. Am. j. Hot. 44: 704, 1 957. 



40. Wardrop, a. B. Personal communication. 



41. Wardrop, A. B. Tappi 40: 225, 1957. 



DISCUSSION 



L. Lorand, S. M. Siegel, A. Marshak, D. A. Marsland, A. D. McLaren 



Dr. Lorand: I wonder if the melanin isolated from quinone-fibrin is free of protein. 

 The tanning effect of quinone could perhaps be eliminated by blocking the free amino 

 group of fibrins (Mihalyi and Lorand, Hung, acta phystol., 1948). 



Dr. Siegel: Permit me to comment first that I would prefer to retain the term 

 'polyquinone' for these products; hence reserving judgment on the polymers as mela- 

 nins, although they are undeniably melanin-like. All extracted polyquinones have 

 proven to be N-free whereas residual pigment solubilizable only by proteolysis (tryp- 

 sin) is firmly associated with peptides or amino acids, hence contains organic N. An 

 amino block would be useful, if matrix activity is not destroyed. 



Dr. Marshak: Does the distribution of lignin formation within the protoxylem ele- 

 ments follow a pre-existing pattern (e.g., annuli and helices of varying pitch) of pectic 

 acid distribution on the walls of cells of developing embryos and seedlings? 



Dr. Siegel: The one serious limitation to the lignin model system lies in the fact 

 that all cells in a tissue slice are flooded with reactants, hence any active surface will 

 participate in lignin deposition, even if in a region not normally receiving precursor. 

 Thus any detailed vascular architecture may be obscured. With respect to such a fine 

 adherence to pattern in nature, I know of no observations, although I expect that 

 Wardrop's group (CSIRO, Australia) will have an answer shortly. 



Dr. Marsland: /) I seem to remember that eugenol is listed as displaying an unusu- 

 ally high compressibility in the range of pressure up to about 10,000 atmospheres. Do 

 you think that this might indicate polymerization by pressure? 2) As to the high 

 activity of starch as the catalyst of lignin formation, is it true that the envelope which 

 naturally covers the starch grain may have a lignin component in its structure? 



Dr. Siegel: /) Presumably, pressure alone could serve as an orienting factor, as 

 could shear or other mechanical agents, but in the ordinary chemical sense, I doubt 

 that pressure alone could bring about polymerization, as the energy would involve at 

 least meeting the level of C-H bond dissociation energies for homolytic cleavage. In 

 the broad sense, including H-bonded structures and crystals in the term 'polymer,' as 



