158 IfHliJ STORY OF THE PLANTS. 



further. We saw reason to believe in a previoufci 

 chapter that petals were originally sepals, flat- 

 tened and brightly coloured, and told off for the 

 special attractive function. Just in the same 

 way the ray-florets of the daisy, the sunflower, 

 the single dahlia, and the aster are florets which 

 have been flattened and partially or wholly 

 sterilised in order to act as allurements to 

 insects. The ray-floret acts for the compound 

 flower-head as the petal acts for the individual 

 blossom. 



In many other families of plants besides the 

 composites we get foreshadowings, so to speak, 

 of this mode of procedure. The outer flowers of 

 a cluster, be it head or umbel, are often rendered 

 larger so as to increase the effective attractive- 

 ness of the whole ; and sometimes they are 

 sacrificed to the inner ones by being made 

 neuter or sterile, that is to say, being deprived 

 of stamens and pistil. Thus in cow-parsnip, 

 which is a member of the same family as the 

 carrot and the hemlock, the outer flowers of each 

 umbel are much larger than the central ones, 

 while in the wild guelder-rose the central 

 flowers alone are fertile, the outer ones being 

 converted into mere expanded white corollas 

 with no essential floral organs. But it is the 

 composites that have carried this process of 

 division of labour furthest, by making the ray- 

 florets into mere petal-like straps, which do no 

 work themselves, but simply serve to attract the 

 fertilising insects to the compound flower-head. 



An immense number of these composites with 

 flattened ray-florets grow in our fields or are 



