THE SHAPES OF FLOWERS. 171 



towards the bilateral shape. A like result occurs under like 

 conditions in Rhododendrons and Azaleas. The Verbena, too, 

 furnishes an illustration of radial flowers rendered slightly 

 two-sided by the slight two-sidedness of their relations to 

 other flowers in the cluster. And among the Cruciferce a 

 kindred case occurs in the cultivated Candytuft. 



Evidence of a somewhat different kind is offered us by 

 clustered flowers in which the peripheral members of the 

 clusters differ from the central members; and this evidence 

 is especially significant where we find allied species that do 

 not exhibit the deviation, at the same time that they do not 

 fulfil the conditions under which it may be expected. Thus, 

 in Scabiosa succisa, Fig. 250, which bears its numerous small 

 flowers in a hemispherical knob, the component flowers, 

 similarly circumstanced, are all equal and all radial; but in 

 Scabiosa arvensis, Fig. 251, in which the numerous small 

 flowers form a flattened disk 

 only the confined central ones ^ 

 are radial: round the edge the 

 flowers are much larger and 

 conspicuously bilateral. 



But the most remarkable 

 and most conclusive proofs of these relations between forms 

 and positions, are those given by the clustered flowers called 

 Umbelliferce. In some cases, as where the component flowers 

 have all plenty of room, or where the surface of the umbel is 

 more or less globular, the modifications are not conspicuous; 

 but where, as inViburnum, CJicerophyllum, Anthriscus, Torilis, 

 Caucalis, Daucus, Tordylium, &c., we have flowers clustered 

 in such ways as to be differently conditioned, we find a num- 

 ber of modifications that are marked and varied in propor- 

 tion as the differences of conditions are marked and varied. 

 In Chcerophyllum, where the flowers of each umbellule are 

 closely placed so as to form a flat surface, but where the 

 umbellules are wide apart and form a dispersed umbel, the 

 umbellules do not differ from one another ; though among the 



