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2. C. P. Whittingham, “Chem. & Biochem. of Plant Pigments,” Vol. 1, ed. by T. W. Goodwin, Adademic Press Inc., London, 1976, p. 624.
3. B. C. L. Weedon, “Carotenoids,” ed. by O. Isler, Birkhäuser Verlag Basel, 1971, p. 267.