72 
Dicotyledons with Gamopetalous Flowers — Convolvulacece. 
Stem rarely shrubby and erect in a few exotic species ; in Dodder ( Cuscuta ) very slender, thread-like and 
twining, attaching itself to nurse-plants by numerous minute disks, each of which emits a root-fibre by which it absorbs 
nourishment from the nurse, and so is enabled early to become independent of the earth in which it originated on 
germination of the seed. 
Flowers axillary, pedunculate ; with a pair of leafy bracts immediately under and inclosing the calyx in White 
and Sea Bindweed ( Galystegia sepium and C. Soldanella ); in small sessile clusters in Dodder ( Guscuta ). 
EMBRYO, with folded cotyledons in a thin albumen ; in Dodder spirally twisted within abundant albumen and 
destitute of cotyledons. 
USES, &c.—Many Convolvulacese are characterised by a milky juice, and more or less of a resinous substance 
to which the medicinal value of some of the species is due. Two of the more important species in medicine are the 
Jalap-affording species of Convolvulus , indigenous in Mexico, and Scammony, the latter a Convolvulus (C . Scctm- 
monia) of the Levant. In the Batatas or Sweet Potato, the root of Batatas eclulis y this resin is absent or inert, and 
the abundant farinaceous matter which it contains renders it a valuable article of food in tropical countries, where it 
substitutes the Potato cultivated in temperate regions. Most of the Convolvulaceae bear very beautiful though short¬ 
lived flowers, and several are in general cultivation, as Major Convolvulus ( Pharbitis purpurea) , a common tropical 
weed; Minor Convolvulus (Convolvulus tricolor ), introduced from Southern Europe; and, in plant-houses, several 
species of Ipomcea , Batatas , and Argyreia. 
Natural Order 
POLEMONIACETi. Tab. 60. 
Diagnosis. —Herbs with alternate or opposite leaves. Calyx 5-lobed. 
Corolla hypogynous, regular. Stamens epipetalous, as many as corolla- 
lobes and alternate with them. Ovary 3-celled ; stigmas 3. 
