Nature and development of plants . separation of some of the genera from theopen flowers of the Umbellales which have also arrived at thesame stage of development, page 432. This would not necessarilvimply a relationship, since it repeatedly happens both amongplants and animals that identically similar structures arise ingroups in no way related. From these simple flowers that may 45Q THE RUB TALES be no more sympetalous than certain genera of the carrot order,we pass to more pronounced tubular forms in the bluets (Hous-tonici), buttonbush (CephahuitJius), twin flower (Linnaea, , C), sn
Nature and development of plants . separation of some of the genera from theopen flowers of the Umbellales which have also arrived at thesame stage of development, page 432. This would not necessarilvimply a relationship, since it repeatedly happens both amongplants and animals that identically similar structures arise ingroups in no way related. From these simple flowers that may 45Q THE RUB TALES be no more sympetalous than certain genera of the carrot order,we pass to more pronounced tubular forms in the bluets (Hous-tonici), buttonbush (CephahuitJius), twin flower (Linnaea, , C), snowberry (Symphoricarpiis) and finally to irregularand even labiate types as in the honeysuckle {Louieera. ), valerian, teasel (Dipsacits) and scabious (Fig. 336). Itis noteworthy that in the three latter genera the flowers becomemassed in a dense inflorescence, known as a head, which are sub-tended by modified leaves, the involucre (Fig. 336) and the pistilsare reduced to a single fertile carpel with two-lobed style. These. Fig. 336. Advanced forms of the Rubiales: A, inflorescence of Scabiosa,at the right showing the involucre, in. B, a single flower enlarged, show-ing the somewhat irregular corolla. At the right the sectional view ofthe flower shows the calyx, ca, terminating in bristle-like teeth; br, bract-like cup surrounding the calyx. C, irregular flower of valerian—11, nectarsac; ca, rudimentary calyx, which matures in the fruit as a mass of deli-cate feathery organs, known as the pappus. variations will become very prominent in the next order. TheRubiales are an important tropical group and furnish the coffee(Coffea) and the cinchonas which yield such drugs as quinineand calisava. DEVELOPMENT OF PLANTS 45i 154. Campanulales, the Bellflower Order.—This order marksthe culmination of the tendencies that we have seen steadilyprogressing through the monocotyledons and the variations have been of so peculiar and successful a naturethat no group of
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