LAW OF PROGRESSIVE COLOURATION. 47 



lucerne, are likewise purple or blue. But in the 

 largest and most advanced types, the peas, beans, 

 vetches, and scarlet runners, we get much brighter and 

 deeper colours, often with more or less tinge of blue. 

 In the sweet-peas and many others, the standard 

 frequently differs in hue from the keel or the wings 

 a still further advance in heterogeneity of colouration. 

 Lupines, sainfoin, everlasting pea, and wistaria are 

 highly evolved members of the same family, in which 

 purple, lilac, mauve, or blue tints become distinctly 

 pronounced. The colouration of the Papilionacece, 

 however, does not as a whole illustrate the general law 

 so well as that of many other groups. 



When we pass on to the Corolliflora, or flowers in 

 which the originally separate petals have coalesced 

 into a single united tube, we meet with much more 

 striking results. 



Here, where the very shape at once betokens high 

 modification, yellow is a comparatively rare colour 

 (especially as a ground-tone, though it often comes out 

 in spots or patches), while purple and blue, so rare 

 elsewhere, become almost the rule. 



The family of Campanulacecs y or bluebells, forms an 

 excellent example. Its flowers are usually blue or 

 white, and the greater number of them, like the hare- 

 bell (Campanula rotundifolia] and the Canterbury bell 

 (C. media), are deep blue (Fig. 1 6). We have nine British 

 species of the genus, varying from pale sky-blue to ultra- 

 marine and purplish cobalt, with an occasional relapse 

 to white. Rampion and sheep's bit, also blue, are 

 clustered heads of similar blossoms. The little blue 

 lobelia of our borders, which is bilateral as well as 

 tubular, belongs to a closely-related tribe. One of 



