An English writer. Mr. Alfred Russell Wallace, notes that chlorophyll is not a simple green pigment, but that it really consists of at least seven distinct substances, varying in color horn blue to yellow and orange; and that they differ in their proportions in the chlorophyll of different plants, have different chemical reactions, are differently affected by light, and give distinct spectra, lie suggests the collective name chromophyll as a proper one for designating the presence of these various pigments.
Kerner and Oliver in their Natural History of Plants state that 14The chemical composition of colouring matters is yet little known. and it is possible that at present a whole group of them is collected together under the name anthocyanin," * and that this substance "appears red in the cell sap in the presence of acids, blue when no acids are present, and violet when the amount of tree acids is but small. It there is an abundance of yellow granules together with the acid, red anthocyanin, the leal assumes an orange color."
Mr. |ustus Watson Folsom, in an article on "Autumnal Changes in Leaves" (Garden and Forest, Vol. VIII, p. 392), says:
" A green leaf, or an alcoholic extract of one, viewed through a spectroscope, shows a band of light, or spectrum, which is very characteristic; its dark intervals or absorption bands, resembling those of no other substance. If, now, we mix benzine with our green solution of chlorophyll which we have obtained by soaking, say, elm leaves in alcohol, the liquid separates into two layers, the upper of bluish-green benzine, and the lower of yellow alcohol. These two solutions give different spectra, proving them different substances. Our chlorophyll, then, was a mixture of at least two substances, or, more likely, a chemical compound which broke into two of its constituent compounds, the yellow one being called xanthophyll. Now, this separation presumably occurs when green leaves turn yellow, as is suggested by a simple experiment. If our alcoholic extraction from elm leaves has not been kept in darkness and sealed from the oxygen of the air, it has rapidly decomposed, turning from green to yellow that is, the green constituent fades away first, gradually revealing the yellow one, which, by the way, some consider the equivalent of the etiolin that always precedes the first formation of the green pigment."
* From the Greek words meaning flower and blue.
Mr. Joseph Wharton, in an article, "Observations upon Autumnal Foliage (American Journal of Science, Vol. 47. p. 253), says that the distinguished French chemist Fremy " separates chlorophyll, when dissolved in alcohol, into two coloring matters, by submitting it to a mixture of ether and chlorohydric acid; the former takes up the yellow matter (phylloxanthin), the latter the blue matter (phyllocyanin), each liquid having distinctly the yellow and the blue color respectively, which being mixed by shaking together form a leal green. 1 he yellow coloring matter of new sprouts and of etiolated leaves contains phylloxanthin, capable of being developed into chlorophyll; in autumnal yellow leaves the phyllocyanin has been destroyed. The yellow matter, Fremy supposes to be more stable than the blue."
Mention is also made in scientific works of chemists who succeeded m extracting from green leaves pigments of various colors in the form of dried, powdery substances.
All these explanations, simply Stated and divested of technical phrases, might read something like this: The substance in a live leaf contains blue and yellow pigments, and, as is well known, these colors when mixed form green. When, through failing vitality the action of these pigments is no longer restrained by the presence of chlorophyll, their colors become apparent. True, no one ever saw a blue leal ; but this color, under the action of the acid remaining in the cell-sap of the leaf, will be stained red. If the yellow substance alone remains the leaf will display that color: and with acids, orange. If the pigmentary substances are absorbed before the leaf falls, the brown walls of the empty cells will give it a russet tint. This explanation is not scientific, and it may not be entirely accurate; but it is fairly deducible from the various and varying statements of the botanists and chemists who have made this subject a matter of scientific research.