394 



COLOURS OF FLOWERS. 



and green, as composed of blue and yellow, is intermediate between 

 them. White is considered as depending on absence or extreme 

 dilution of the colouring principles, while brown or black depends 

 on their accumulation or concentration. Even in white flowers there 

 will be seen a slight admixture of a yellowish or bluish tint. 



Oreen. 



Some, starting from greenness, as a state of equilibrium between 

 the two series, pass through the blue and violet- to red, by a process 

 of oxidation, while the transition from red to orange and yellow has 

 been traced to deoxidation. As illustrations of the cyanic series may 

 be mentioned all, or nearly all, the species of Campanula, Phlox, 

 EpUobium, Hyacinth, Geranium, Aaagallis ; of the xanthic series, 

 Cactus, Aloe, Cytisus, Oxalis, Kose, Verbascum, PotentDla, CEnothera, 

 Ranunculus, Adonis, Tulip, Dahlia. 



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 wUl 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 yeUow species. It seems, however, to be applicable to individual 

 species ; thus the Dahlia, belonging to the yellow series, may pass 

 through all the varieties of that series, but has never been produced of 

 a blue colour ; so also with the Tulip, the Rose, etc. Even in the 

 case of species, however, there are anomalies. Thus the rule does not 

 apply to such plants as Myosotis versicolor and Dendrobium sanguino- 

 lentum, where there are different yellow and blue colours on the 

 coroUa. 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. ' 



Changes are produced in the colour of flowers by bruising and 

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

 brown, while those of Oalanthe veratrifolia and Bletia TankerviUse 

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

 black colour ; this is particularly the case with Orchidacese, Melam- 

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

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



