328 COLOURS OF FLOWERS. 



Aloe, Cytisus, Oxalis, Rose, Verbascum, Potentilla, (Enothera, Ranun- 

 culus, Adonis, Tulip, Dahlia. 



681. Plants belonging to either series, vary in colour usually by 

 rising or falling in the series to which they belong, and not by passing 

 from one to the other. Thus, a plant belonging to the blue series 

 does not usually become yellow, nor does one in the yellow series 

 change into a pure blue. This remark will not apply in all cases, 

 although it is generally true. It cannot be said to hold good in 

 regard to genera, as at present determined; thus, in the genus Gentian, 

 there are blue and yellow species. It seems, however, to be applicable 

 to individual species; thus, the Dahlia belonging to the yellow series 

 has been made to pass to all varieties of that series, but has never 

 been produced of a blue colour; so also with the Tulip, the Rose, &c. 

 Even in the case of species, however, there are anomalies. Thus, the 

 rule does not apply to such plants as Myosotis versicolor and Dendro- 

 bium sanguinolentum, where there are different yellow and blue colours 

 on the corolla. Notwithstanding, however, all the exceptions, the 

 general law already mentioned as to the variation of colour in flowers, 

 seems to be founded on correct observations. 



682. Changes are produced in the colour of flowers, by bruising and 

 injuring the petals. The pure white flowers of Camellia easily become 

 brown, while those of Calanthe veratrifolia and Bletia Tankervillae 

 assume a deep blue. By drying, many flowers become of a brown or 

 black colour: this is particularly the case with Orchidaceae, Melam- 

 pyrum, and Orobus niger. It would appear to depend on the com- 

 bination between the colouring principle and the oxygen of the air, 

 and may in some cases be traced to the existence of tannin, gallic acid, 

 and iron. Blue flowers, under the process of desiccation, are often 

 whitened. Ipomcea Learii, in drying, changes from blue to red. 



683. Remarkable changes take place in the colour of some flowers 

 during the course of the day. The flowers of the common pink Phlox, 

 early in the morning, have a lightish blue colour, which alters as the 

 sun advances, and becomes bright pink. The CEnothera tetraflora has 

 white flowers which change to red. Hibiscus variabilis has its flowers 

 white in the morning, pink at noon, and bright red at sunset. The 

 colour of many flowers of Boraginaceae, before expansion, are red; after 

 expansion, blue. The bracts of Hakea Victoria are yellowish-white in 

 the centre the first year; the second year, what was white becomes a 

 rich golden yellow; the third year, the yellow becomes rich orange; 

 the fourth year, the colour becomes blood-red; the green portion of 

 the bracts becomes annually darker. It has been stated that soils 

 have an effect on the colour of flowers. The flower of the common 

 Hydrangea hortensis may be changed from pink and rose-coloured to 

 blue, by growing the plant in certain kinds of loam and peat earth. 

 Alum in the soil is said to produce a similar effect. 



