LA W OF PROGRESSIVE COL O URA TION. 5 3 



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. 18. Vertical section of head of daisy (Bellis pe rennls) \ 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 corymbiferous types, such 

 as the corn-marigold (Chrysanthemum segetum), the 

 sun-flower (Helianthus annuus], and the ragwort 

 (Senecio jacobced}, are yellow like the central flowers. 

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

 may-weed (Anthemis cotula, Chrysanthemum leucan- 

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



