The colouring matter of red roses

As examination of the petals of the red rose “George Dickson,” has shown that the anthocyen pigment contained therein is the cyanidin glucoside, cyanin. It is present to the extent of about 9—10 per cent. by weight of the dried petals, and exists in the petals as an oxonium salt ( i. e ., in combination with a plant acid). A yellow glucoside sap-pigment also occurs in the same flowers, but beyond the fact that it has been shown to be capable of producing an anthocyan, by reduction, and that it is not a glucoside of the flavonol myricetin, it has not been further identified, on account of the small quantity present. Further work may show it to be a glucoside of quercetin, and corroborate the work of Dr. Everest, on the purple-black viola, in which it was shown that an anthocyan (“violanin”) and the flavonol glucoside from which it could be produced, by reduction (a glucoside of myricetin), are present, side by side, in the same flowers. This would be additional evidence in favour of the hypothesis that “anthocyans are produced, in nature, by the reduction of the flavonols.” It is interesting to note that this rose, grown in Australia, contains the same colouring matter as was isolated by Willstätter and Nolan from the rose known as “Rosa Gallica,” grown in Europe, and shows how widely these colouring matters are distributed in nature. The rose “George Dickson” was chosen for this investigation on account of its deep red colour, which would indicate a fairly large percentage of the anthocyan pigment. The flowers from which the petals were gathered were grown by Mr. G. Knight, at his nursery, Parramatta Road, Homebush, and his generosity in supplying me with sufficient material enabled the work to be successfully accomplished.

The production of anthocyanins and anthocyanidins

The idea that the anthocyan pigments are closely related to the flavone and flavonol glucosides is by no means new. Attempts to solve the problem of their relationship have come chiefly from botanists, and, as a result of their researches, a number of hypotheses have sprung up around which quite considerable controversy has been centred. Miss Wheldale puts forward the suggestion that anthocyan pigments are the oxidation products of colourless or faintly coloured chromogens; and that these chromogens are products of hydrolysis of glucosides present in the tissues of the plant (probably glucosides of flavone or flavonol derivatives). The hydrolysis of the glucoside she considers as essential to the production of the anthocyan pigment. She represents the changes taking place by means of the following equations :— Glucoside + water ⇆ chromogen + sugar. Then— Oxidation of chromogen → anthocyan pigment.