DEVELOPMENT OF PLANTS 



483 



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 

 Rubiales are an important tropical group and furnish the coffee 

 (Coffea) and the cinchonas which yield such drugs as quinine 

 and calisaya. 



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

 at the right showing the involucre, in. B, a single fl'ower 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-Hke 

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

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

 ery organs, known as the pappus. 



154. Campanulales, the BelMower Order. — This order marks 

 the culmination of the tendencies that we have seen steadily 

 progressing through the monocotyledons and the dicotyledons. 

 The variations have been of so peculiar and successful a nature 

 that no group of plants are so widely distributed and in the 

 more specialized families of so common occurrence. Over 

 14,500 species are known. The parts of the epigynous flowers 

 are arranged in four whorls of usually five members each. The 



