15G 



MORPHOLOGICAL DEVELOPMENT. 



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



flowers form a flattened disk, 



V, only the confined central ones 



>^ ''^^'^S-^ are radial : round the edge the 



■ Vii " 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 

 Umbe'Ji/ene. 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 in Viburnum, Chasrophyllum, Ajithriscus, lorilis, 

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

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

 ber of modifications that are marked and varied in propor- 

 tion as the diflerences of conditions are marked and varied. 

 In Ohmrophyllum, 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 imibel, the 

 umbellules do not difier from one another ; though among the 

 flowers of each umbellule there are decided diflerences — the 

 central flowers being small and radial, while the peripheral 

 ones are large and bilateral. But in other genera, where not 

 only the flowers of each umbellule but also the umbellules 

 themselves are closely clustered into a flat surface, the umbel- 

 lules themselves become contrasted; and many remarkable 

 secondary modifications arise. In an umbel of Heracleum, 

 for instance, there are to be noted the facts : — first, that the 

 eKternal umbellules are larger than the internal ones ; 

 second, that in each umbellule the central flowers are less 

 developed than the peripheral ones ; third, that this greater 

 development of the peripheral flowers is most marked in the 

 outer umbellules ; fourth, that it is most marked on the outer 

 s'ides of the outer umbellules ; flfth, that while the interior 

 flowers of each umbellule are radial, the exterior ones are 



