THE MONOPETALOUS ORDERS. 



451 



sists of two plants only, viz. the Alpine Diapensia, and Pyxidan- 

 thera, of the Pine-barrens of New Jersey, &c. 



916 



846. Ord. ConvolvulaceSB (the Convolvulus Family). Twining or 

 trailing herbs or shrubs, often with milky juice ; the leaves alter- 

 nate, and the flowers regular. Calyx of five sepals, imbricated, or 

 usually more or less united, persistent. Corolla supervolute in 

 aestivation (Fig. 363) ; the limb often entire. Stamens five, insert- 

 ed on the tube of the corolla near the base. Ovary free, two- to 

 four-celled, with one or two erect ovules in each cell : styles 

 united, or more or less distinct. Capsule two- to four- (or by oblit- 

 eration one-) celled ; the valves falling away from the persistent 

 dissepiments (septifragal). Seeds large, with a little mucilaginous 

 albumen : embryo curved, and the foliaceous cotyledons usually 

 crumpled. Ex. Convolvulus (Morning-Glory, Bindweed). They 

 all contain a peculiar strongly purgative resinous matter, which is 

 chiefly found in the acrid, milky juice of their thickened or tuber- 

 ous roots. Convolvulus Jalapa, and other Mexican species, fur- 

 nish the Jalap of the shops. The more drastic Scammony is de- 

 rived from the roots of C. Scammonia of the Levant. There is 

 much less of this in those of Convolvulus panduratus (Mechameck^ 

 Man-of-the-Earth, Wild Potato-vine) : while those of C. macrorhi- 

 fcus of the Southern States, which sometimes weigh 40 or 50 pounds, 

 are farinaceous, with so slight an admixture of the peculiar resin 



FIG. 913. Pyxidanthera barbulata, natural size. 914. Pistil, in fruit, and the persistent 

 calyx, enlarged. 915. Corolla and stamens. 916. Same laid open. 917. A separate stamen 

 magnified. 918. Section of the dehiscent capsule. 919. A seed. 



