TilK SHAPES OF FLOWEHS. 



157 



sfO 



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 imsymmetrically 

 placed, are unsymmetrically bilateral.* The like modi- 

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

 able a way, in an umbel of Tordi/lium, Fig. 352. 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 difiier- 

 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-flowoiv 

 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 circimistanced 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 bilatei-al 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. 



