THE SHAPES OF FLOWERS. 



157 



bilateral ; sixth, that this bilateralness is most marked in 

 the peripheral flowers of the peripheral umbellules ; seventh, 

 that the flowers on the outer side of these peripheral 

 umbellules are those in which the bilateralness reaches a 

 maximum ; and eighth, that where the outer umbellules 

 touch each other, the flowers, being unsymmetrically 

 placed, are unsymmetrically bilateral.* The like modi- 

 fications are displayed, though not in so clearly-trace- 

 able a way, in an umbel of Tordylium, Fig. 252. Considering 

 how obviously these various 

 forms are .related to the vari- 

 ous conditions, we should be 

 scarcely able, even in the 

 absence of all other facts, to 

 resist the conclusion that the 

 differences in the conditions 

 are the causes of the differ- 

 ences 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, 

 exemplifies the extremely marked differ- 

 ence that 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 having 



* I had intended here to insert a figure exhibiting these differences ; but as the 

 Cow-parsnip does not flower till July, and as I can find no drawing of the umbel 

 which adequately represents its details, I am obliged to take another instance. 



353 



