THE SHAPES OF FLOWERS. 173 



absence of all other facts, to resist the conclusion that the 

 differences in the conditions are the causes of the differences 

 in the forms. 



Composite flowers furnish evidence so nearly allied to that 

 which clustered flowers furnish, that we may fitly glance 

 at them under the same head. Such a common type of 

 this order as the Sun-flower, exempli- 

 fies the extremely marked difference 

 which arises in many of these plants 

 between the closely-packed internal 

 florets, each similarly circumstanced on 

 all sides, and the external florets, not 

 similarly circumstanced on all sides. 

 In Fig. 253, representing the inner and 

 outer florets of a Daisy, the contrast is 

 marked between the small radial corolla of the one and the 

 larger bilateral corolla of the other. In many cases, how- 

 ever, this contrast is less marked: the inner florets also 

 having their outward-growing prolongations a difference 

 possibly related to some difference in the habits of the insects 

 that fertilize them. Nevertheless, these composite flowers 

 which have inner florets with strap-shaped corollas out- 

 wardly directed, equally conform to the general principle; 

 both in the radial arrangement of the assemblage of florets, 

 and in the bilateral shape of each floret; which has its 

 parts alike on the two sides of a line passing from the centre 

 of the assemblage to the circumference. Certain 



other members of this order fulfil the law somewhat differ- 

 ently. In Centaurea, for instance, the inner florets are small 

 and vertical in direction, while the outer florets are large and 

 lateral in direction. And here may be remarked, in passing, 

 a clear indication of the effect which great flexibility of the 

 petals has in preventing a flower from losing its original 

 radiate form ; for while in C. cyanus, the large outward-grow- 

 ing florets, having short, stiff divisions of the corolla, are 

 decidedly bilateral, in C. scabiosa, where the divisions of the 



