LAW OF PROGRESSIVE COLOURATION. 53 



blossoms (Fig. 18). In short, they are sterilised mem- 

 bers of the compound flower-head, specially set apart 

 for the work of display ; and thus they stand to the 

 entire flower-head in the same relation as petals do to 

 the simple original flower. The analogy between the 

 two is complete. Just as the petal is a specialised 

 and sterilised stamen told off to do duty as an 

 allurer of insects for the benefit of the whole flower, 

 so the ray-floret is a specialised and sterilised blos- 

 som told off to do the self-same duty for the benefit 



Fig. iS.— Vertical section cf head of daisy {Bellis perenms); central florets, yellow ; 



ray florets, white, tipped with pink. 



of the group of tiny flowers which make up the 

 composite flower-head. 



Now, the earliest ray-florets would naturally be 

 bright-yellow, like the tubular blossoms of the central 

 disk from which they sprang. And to this day the 

 ray-florets of the simplest corymbifcrous types, such 

 as the corn-marigold {ChrysantJieimun segetum), the 

 sun-flower {HcliantJms annuus), and the ragwort 

 {Senecio jacoba^d)y are yellow like the central flowers. 

 In the camomile, however, the ox-eye daisy, and the 

 may-weed {Antheinis cotula, Chrysanthemum leucan- 

 t/iemtim, &c.), the rays have become white ; and this, 



