222 
CONVOLVULACEiE. 
are mostly moderate climbers suitable for the bases of pillars, the 
bottom part of walls, or to be grown in pots, and supported by 
rather large wire frames. They delight in rich friable loam, and 
should be frequently syringed while growing, to prevent the 
lodgement of red spider, and to otherwise assist the healthy deve¬ 
lopment of leaves and flowers. 
Among the stove species, the most remarkable is the lovely 
pentanthus, with its brilliant blue flowers, ciliatus , with its 
curious fringed leaves, and delicate rose-coloured blossoms, and 
the noble quinquefulius producing flowers of a pure white and 
purple: these require a brisk growing heat, with plenty of mois¬ 
ture in the active season, and a decided rest in winter. They may 
be stationed in the same manner as the greenhouse kinds, 
though the last named is of much stronger habit than any other. 
The genus Cressa has only one species, C. cretica, a hardy 
annual with white flowers, less beautiful than most other members 
of the order. 
Evolvulus is composed principally of tender annuals, having 
handsome brilliant blue flowers ; they should be sown early in 
spring, and subsequently treated as is usual with plants of the 
same description. The perennial species are adapted for pot- 
culture ; they have a climbing habit of moderate extent, and look 
well on wire trellis. 
Exogonium is a small genus, but important, as it contains the 
plant furnishing the medicinal drug jalap. For a long time an 
erroneous impression prevailed, that it was obtained from the 
Ipomcea machroriza , but Scheide, the botanical traveller, from 
personal examination, verified by other persons engaged in the 
trade of that article, proved that it was obtained, not from the 
hot plains around Yera Cruz, where the Ipomsea is abundant, but 
from the more elevated and cooler districts near Jalapa, and that 
the plant which yields it is the Exogonium purga. It has been cul¬ 
tivated in England since 18*38, and, independent of its interest in 
the above respect, is well worth attention for its intrinsic beauty. 
The stems rise from a roundish tuber, and extend ten or twelve 
feet; the flowers, which are freely produced, are about the size 
of those on the Convolvulus minor , or rather larger, of a rich 
purplish-red, gradually becoming paler towards the throat. The 
other species are filiforme and repandum , both formerly included 
