LA W OF PROGRESSIVE COLOURA TION. 55 



sage (Fig. 19), and basil, which it need hardly be said 

 are great favourites with bees. Ground-ivy (Nepeta gle- 

 chomd) is bright blue ; catmint (Nepeta cataria], pale 

 blue ; Prunella, violet-purple ; and common bugle 

 (Ajuga reptans], blue or flesh-colour. Many of the 

 others are purple or purplish. It must be added that 

 in this family the flowers are very liable to vary 

 within the limit of the same species ; and red, white, 

 or purple specimens are not uncommon in many of 

 the normally blue kinds. 



FIG. 19. Flower of sage (Salvim) visited by bee ; blue. 



The Scropkularinecz and other allied irregular tubular 

 families are mostly spotted, and so belong to a later 

 stage of our inquiry ; but even amongst this group, 

 the Veronica genus has almost always pure blue 

 flowers ; foxglove (Digitalis purpured] is purple; and 

 most of the Broomrapes (Orobanchacece] are more or 

 less bluish. Blue and lilac also appear abundantly 

 in spots or stripes in many species of Linaria, in 

 Euphrasia, and in other genera, 



We have given so much consideration to the Dico- 

 tyledons that the relatively simple and homogeneous 



