J Genetics 21: 125–159 (1929)
The Genetics and Cytology of Dahlia Species
W. J. C. Lawrence

(c) Reactions of anthocyanins and flavones with ammonia and SO2

As indicated on p. 128 the change of colour occurring when white, ivory or yellow petals are fumed with ammonia is as follows:

Petal colour Changes to
White No change
Ivory Lemon yellow
Yellow Intense orange

The ammonia test is a well-known method used for detecting the presence of anthocyanin in plant tissues. If anthocyanin is present a green or bluish colour usually develops upon fuming, though possibly other substances in the cell sap may modify this green or bluish appearance. In addition to the many fumings made with ammonia in the course of these experiments, petals have been bleached with SO2, and the reactions of different flower colours with these two reagents noted.

The observations may be briefly summarised as follows:

SO2.— SO2 does not affect the flavones. It half bleaches the deeper coloured petals and almost entirely bleaches tinged varieties. Penetration is increased if the petal is first fumed in ammonia and then bleached—complete removal of the anthocyanin pigments resulting, thus revealing the flavone ground.

Ammonia.— (a) Magenta and purple flowers give green and bluish-green reactions. (b) Orange and scarlet give an intense reddish-brown coloration. (c) Intermediate forms give intermediate reactions.

The intense reddish-brown which develops when orange or scarlet petals are fumed is of some interest, since this is not typical reaction of anthocyanin with ammonia.

All the other species I have grown conform, after their kind, to the above results.