branches, revolved and twined; but it should be stated that the plant
was not growing vigorously. My plants of Combretum argenteum and C.
purpureum made numerous short healthy shoots; but they showed no
signs of revolving, and I could not conceive how these plants could
be climbers; but at last C. argenteum put forth from the lower part
of one of its main branches a thin shoot, 5 or 6 feet in length,
differing greatly in appearance from the previous shoots, owing to
its leaves being little developed, and this shoot revolved vigorously
and twined. So that this plant produces shoots of two kinds. With
Periploca Graeca (Palm, p. 43) the uppermost shoots alone twine.
Polygonum convolvulus twines only during the middle of the summer
(Palm, p. 43, 94); and plants growing vigorously in the autumn show
no inclination to climb. The majority of Asclepiadaceae are twiners;
but Asclepias nigra only "in fertiliori solo incipit scandere
subvolubili caule" (Willdenow, quoted and confirmed by Palm, p. 41).
Asclepias vincetoxicum does not regularly twine, but occasionally
does so (Palm, p. 42; Mohl, p. 112) when growing under certain
conditions. So it is with two species of Ceropegia, as I hear from
Prof. Harvey, for these plants in their native dry South African
home generally grow erect, from 6 inches to 2 feet in height,--a very
few taller specimens showing some inclination to curve; but when
cultivated near Dublin, they regularly twined up sticks 5 or 6 feet
in height. Most Convolvulaceae are excellent twiners; but in South
Africa Ipomoea argyraeoides almost always grows erect and compact,
from about 12 to 18 inches in height, one specimen alone in Prof.
Harvey's collection showing an evident disposition to twine. On the
other hand, seedlings raised near Dublin twined up sticks above 8
feet in height. These facts are remarkable; for there can hardly be
a doubt that in the dryer provinces of South Africa these plants have
propagated themselves for thousands of generations in an erect