468 



THE RUBIALES 



plants and animals that identically similar structures arise in 

 groups in no way related. From these simple flowers that may- 

 be no more sympetalous than certain genera of the carrot order, 

 we pass to more pronounced tubular forms in the bluets( Hous- 

 tonia), buttonbush (Cephalanthus) , twin flower (Linnaea, Fig. 

 335, C), snowberry (Symphoricarpus) and finally to irregular 

 and even labiate types as in the honeysuckle {Lonicera, Fig. 

 268), valerian, teasel (Dipsacus) and scabious (Fig. 336). It 



Fig. 336. Advanced forms of the Rubiales: A, inflorescence of Scahiosa, 

 at the right showing the involucre, in. B, a single flower enlarged, show- 

 ing the somewhat irregular corolla. At the right the sectional view of the 

 flower shows the calyx, ca, terminating in bristle-like teeth; br, bract-like 

 cup surrounding the calyx. C, irregular flower of valerian — w, nectar sac; 

 ca, rudimentary calyx, which matures in the fruit as a mass of delicate feath- 

 ery organs, known as the pappus. 



is noteworthy that in the three latter genera the flowers become 

 massed in a dense inflorescence, known as a head, which are sub- 

 tended by modified leaves, the involucre (Fig. 336) and the pistils 

 are reduced to a single fertile carpel with two-lobed style. These 

 variations will become very prominent in the next order. The 



