1078
WILDER D. BAXCROFT
(6) LAMM,0 . :.4rkiv Kemi, Mineral. Geol. 18A, No. 2 (1944). (7) LAMM,0 . :Arkiv Kemi, Mineral. Geol. M A , Nd. 9 (1944). ( 8 ) LAMM,0.: Arkiv Kemi, Mineral. Geol. M A , No. 10 (1944). (9) LAMM,0.:Arkiv Kenii, Mineral. Geol. 18B,No. 5 (1941). (10) Lahihi, 0 . :Paper published in honor of T . Svedberg, Upsala, 1944, p. 182. (11) LEWIS,G . N., AND RASDALL, M.:Thermodynamics and the Free Energy of Chemical Substances. RlcGraw-Hill Book Company, Inc., New York (1923). (12) MEIXNER,J.: Ann. Physik [51 39, 333 (1941); 43, 244 (1943). (13) OXSAGER, L . : Phys. Rev. 37, 405 (1931). ONSAGER, L . , AND Fuoss, R . &I.: J. Phys. Chem. 36, 2689 (1932). (14) THIESEK,11.:Verhandl. deut. physik. Ges. 4 , 348 (1902).
THE BIOCHEMISTRY O F PLAiCT PIGMENTS WILDER D. BANCROFT Cornell rniuersity, Ithaca, .Vew Y o l k Received B p r i l 29, 194Y
A great deal of work has been done on the chemistry of plant pigments (l), much of it first class. When it comes to the biochemistry of plant pigments our scientific knon-ledge is still very unsatisfactory. This is apparently because the problem is one which should be attacked by chemists and botanists n-orking conjointly. This has not yet happened. I t is possible that the botanist could learn enough chemistry to enable him to dispense with the chemist; but no botanist has clone that. It is probable that the chemist could learn enough botany to enable him to dispense with the botanist; but no chemist has yet done that. Lycopene, Cd0HS6,is the red pigment of the tomato. "Lycopene has also been found in hips (Rosa c u n i n a ) , in thc ripe fruits of Tamus com(C,'hristmns rose), i n deadly nightshade (Solanuw riulcomara), in the fruit of the watermelon (C'ucutnis cilrullus), in the berries of d l r i i m i n u c i i l a t u t i i , in the apricot (Prunus u m e n i a c a ) , in bryony fruit (Bryonia dioica), in the golden flowers of the marigold (Calendula o$kinaZis), in the fruit of lily-of-the-valley (Cowiilluria m a j a l i s ) , i n Kaki fruit (Dius,iUru,3 K u k i ) , in tropical fruits, in the dark orange blossom of Dimovlihoteca aurantia, i n Citrus yratidis, in Passiflorn c o e r u l e a , and in bacteria, ae in the thiocustio baclereuiii." (10) miitiis
Apart from lycopene the red and many of the blue regetable pigments are anthocyanins or anthocyans. They are all derivations of 2-phenylbenzopyrylium salts and all, with the exception of a fev amino derivatives, are hydroxy derivatives existing in the plant usually as glycosides. X11 blue flowers turn red when acidified. Some red flowers, but not all, pass through blue \\.hen treated Xvith ammonia. It is not known \That stabilihes the blue and ivhether it is always the same substance or mixture of substances. I t is now known that crude extracts of the anthocyans contain copigments such as tannin, gallic acid, etc., which possess the ability to intensify or modify the color. Thus the glucoside of 2-hydroxyxanthone is an active copigment for cyanin,
BIOCHEMISTRY OF PLAIVT PIGMENTS
1079
and the inner violet parts of the fuchsia flower contain tannin and are thus distinguished from the external red portions. The formation of complexes with organic materials or, for example, with iron, has a greater effect on the color of varying varieties than the acidity of the cell sap, or so say Mayer and Cook. The fact that aluminum sulfate causes hydrangeas to come blue must be because of a marked adsorption of alumina, though this has not yet been shown by the chemist, so far as I can learn. I am hoping that Professor H. B. Weiser of Rice Institute will some clap show this to be true. Selective adsorption is colloid chemistry. I have placed flowers of pink hydrangeas in a saturated solution of alum. The petals turn blue as they should; but it is a slow operation, requiring days. The alum appears to go in through the stems and not through the face of the petals. With a dilute solution of alum there appears to be no change of color; but that may have been Fiecause I did not allow enough time. I n the growing plant there cannot be a saturated solution of alum, but the time factor is very different. There appears also to he a partial bleaching of the parts of the petals which are still pink, and I cannot offer any explanation for that a t present. I n hydrangeas grown in a greenhouse some of the petals or parts of them come white or nearly so, without there being any obvious reason for it. I do not like to suggest selective mutations, because I do not knon. esactly n h a t I mean by the term. I think that the u-hite hydrangeas are a different variety ( l ) , because they do not turn red or pink el-en when growing outdoors. There are numerous details about hydrangeas which need studying. I do not know whether alum affects other red flowers, and, if not, why not. I wonder what alum xould do with red Althaea and with G'erariium maculatum Linnaeus. Though it has nothing to do n i t h colors, an interesting fact is cited by the Old Dirt Dobber (20) : "The blossom heads of caulifloiver should be protected from sunlight in order to develop the desirable nhite curd. ;1s soon as the head begins t o form all of the leaves should be gathered up'and tied loosely at the top in order to shut out the light. Tying too tightly is liable to cramp the heads." People are pretty ]vel1 agreed that the anthocyanins become more intense in color as one moves up a mountain from sea level. Bonnier (2) says that from studies made in the -1ustrian Alps he concludes that most floivers are deeper in color the higher they grou and that uhite floivers tend to liecome pink. 'Tlw effect of altitude is very miirked n-ith Jfyosolis silvalica, C'ainpanula rot
