BUTTERCUP EVOLUTION 



of advancement, for with the more complex adapta- 

 tions to insure fertihsation the numerous single- 

 seeded carpels characteristic of the family can be 

 dispensed with. This latter feature is conspicuous 

 in all the advanced types ; indeed, in the highest 

 forms there are rarely more than one to three 

 carpels, so secure are they of fertilisation. 



The Larkspurs (Delphinium) show a still 

 higher evolution. Their calyx is coloured blue, is 

 large and showy, and prolonged into a spur at its 

 base. There are only two petals in the British 

 species, and these have both developed into spur- 

 like nectaries, and even these have combined at 

 their base. The spurred nectaries are enclosed 

 within the calyx spur ; and in this way the honey 

 is protected from short-tongued bees which cannot 

 legitimately reach the nectar, but which, instead of 

 entering the flower and assisting in its fertilisation, 

 would bite open the spur to get at the honey. It 

 may be, too, that the calyx spur possesses some 

 distasteful property. Its tissues are certainly 

 tougher for the bee or wasp to penetrate than the 

 nectary tubes would be ; at all events, it is dis- 

 couraging to such robbers to find that, after all 

 their work, there is another spur within. 



Why is the larkspur more highly evolved than 

 the columbine, seeing that it has lost three of its 

 petals while the columbine has retained its five ? 

 Well, the larkspur has lost three of its petals 

 because the complex adaptations of its structure 

 have permitted it to economise in this manner. 

 In Chapter XL we observed how the one stamen of 



183 



