668 A TEXT-BOOK OF BOTANY. 



The leaves and bark of the cultivated oleander {Neriuni Olean- 

 der) contain the glucoside oleandrin, resembling digitalin in its 

 action ; a fluorescent principle, and probably several other 

 principles. 



The common periwinkle ( Vinca minor) contains the principle 

 vincin, which is supposed to be a glucoside and which probably 

 occurs in other species of Vinca. 



e. ASCLEPIADACEyE 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 pollinia. Few of the plants are of any economic 

 importance. The latex of the stems and the hairs of the seeds are 

 deserving of attention. Pleurisy root, which was formerly offi- 

 cial, is obtained from Asclepias tiiberosa, a plant growing in the 

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

 that have orange-colored flowers (Fig. 365). 



CoNDURANGO is the bark of Marsdenia Cundtirango, a liane of 

 Ecuador and Colombia. 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 an amorphous glucoside ; an unsatu- 

 rated alcohol occurring in large prisms; and a volatile oil (0.3 

 per cent.). 



V. 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 regular 

 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. 366). 



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 



