28 THE COLOURS OF FLOWERS. 



more sought after by insects than any others of their 

 family. 



Now, if we look closely at these facts, we see that 

 they have several interesting implications. The yellow 

 potentillas have the very simplest arrangement of the 

 carpels in the whole family, and their fruit is of the 

 most primitive character, consisting only of little dry 

 separate nuts. They have altered very little from 

 their primitive type. Accordingly, almost all the 

 genus is yellow ; a very few members only are white ; 

 and these in their habits so far vary from the rest that 



FIG. 8. Vertical section of dog-rose {Rosa). Pink. 



they have very erect flowers, and three leaflets instead 

 of five or more to each leaf. One of them, the straw- 

 berry, shows still further marks of special differentia- 

 tion, in that it has acquired a soft, pulpy, red fruit, pro- 

 duced by the swelling of the receptacle, and adapted 

 to a safer mode of dispersal by the aid of birds. This 

 group, however, including Geuin, cannot claim to be 

 considered the earliest ancestral form of the roses, 

 because of its double calyx, which is not shared by 

 other members of the family, as it would be if it had 

 belonged to the actual, common ancestor. In that 



