36 THE COLOURS OF FLOWERS. 



reduced to five, the regularity of number being itself 

 a common mark of advance in organization. Various 

 columbines accordingly range from red to purple and 

 dark blue. Our English species, A. vulgaris, is blue 

 or dull purple, though it readily reverts to white or 

 red in cultivated varieties. Even the columbine, 

 however, though so highly specialised, is not bila- 

 terally but circularly symmetrical. This last and 

 highest mode of adaptation to insect visits is found in 

 larkspur {Delphinium ajacis), and still more developed 

 in the curious monkshood [Aconitiun napellus, Fig. 12). 



Fig. II. — Petal of columbine produced into a honey-bearing spur. 



Now larkspur is usually blue, though white or red 

 blossoms sometimes occur by reversion ; while monks- 

 hood is one of the deepest blue flowers we possess. 

 Both show very high marks of special adaptation ; 

 for besides their bilateral form, Delphinium has the 

 number of carpels reduced to one, the calyx coloured 

 and deeply spurred, and three of the petals abortive ; 

 while Aconitum has the carpels reduced to three and 

 partially united into a compound ovary, the upper 

 sepals altered into a curious coloured hood or helmet, 

 and the petals considerably modified (Fig. 13). All 

 these very complex arrangements are defintely corre- 



