CLASSIFICATION OF ANGIOSPERMS. 365 



e. ASCLEPIADACE^ OR MILKWEED FAMILY.— The 

 plants somewhat resemble those of the Apocynaceae. The flower, 

 however, is distinguished by having distinct styles, a 5-lobed 

 corona connecting the corolla and stamens, which latter are mostly 

 monadelphous, and pollen grains that are coherent, forming char- 

 acteristic pairs of poUinia. It is rather remarkable that while this 

 family contains a large number of plants that are used in medicine 

 none of them are official. Pleurisy root, which was formerly 

 official, is obtained from Asclepias tuberosa, a plant growing in 

 the Eastern United States and one of the two members of this 

 genus that have orange-colored flowers. The root is more or less 

 fusiform (Fig. 173), about i or 2 cm. thick, and is usually cut into 

 longitudinal pieces. In the dried condition it is light brown exter- 

 nally, more or less irregular, with a tough fracture and a bitter, 

 slightly acrid taste. The active principle is the glucoside asclepia- 

 din. A similar principle is found in the root of other species of 

 Asclepias. 



CoNDURANGO is the bark of Marsdenia Cundurango, a liane of 

 Ecuador and Columbia. It occurs in quilled pieces, the bark being 

 from 2 to 6 mm. thick. Externally it is brownish-gray and with 

 a more or less scaly cork. The taste is bitter, acrid and aromatic. 

 The drug contains two or three glucosides and a resinous sub- 

 stance. 



IV ORDER POLEMONIALES OR TUBIFLOR^. 



This is a large order of plants, which are mostly herbaceous. 

 The leaves are either opposite or alternate ; the flowers are reg- 

 ular or irregular, the stamens being usually adnate to the corolla. 



a. CONVOLVULACE^ OR MORNING-GLORY FAM- 

 ILY. — The plants are mostly herbs or shrubs, frequently twining 

 (to the left). They are found mostly in the Tropics, but quite a 

 number of genera occur in temperate regions (Fig. 174). 



Exogonium Purga is a perennial twining herb with distinctly 

 veined, cordate leaves; purple flowers with the stamens exserted, 

 and occurring in cymes. The fruit is a 2-locular capsule. The 

 plants produce slender rhizomes with tuber-like roots, these being 

 used in medicine (p. 451). 



