Factors determining petal colour of baccara roses III: Effect of the ratio between cyanin and pelargonin

The changes in colour and in the pigment concentration of the two sides of Baccara rose petals which occur when plants are grown under various temperature regimes, were examined. The inner side of the petal is redder and the predominant pigment is pelargonin whereas the outer petal surface tends to 'blue', and, the predominant pigment on this side is cyanin. The cyanin: Pelargonin ratio on the outer side of petals increased three-fold under the influence of low temperatures.The outer surface of petals growing for a long period under low tempertaures was 'blue' when compared with the red petals which had been subjected to low temperatures for a short period. The cyanin: pelargonin ratio of 'blue' petals was higher than that of red petals. Total pigment content was similar in both types of petal. Flowers grown under high temperatures 'blued' without a concomitant fall in the cyaninpel: argonin ratio.Examination of colour solutions in which the ratio between cyanin and pelargonin was varied revealed that the colour of the solution became bluer as this ratio increased.We suggest that the 'blueing' of Baccara rose petals is caused primarily by a dilution of the cyanin content, but when the ratio between cyaniri and pelargonin increases sharply, 'blueing' may also occur in dark flowers in which the total pigment content did not diminish.