232 
SLEEP OF LEAVES. 
The phenomenon to which we allude is called the sleep of plants. This 
consists in a periodic change in the position of an entire leaf, or of the several 
leaflets of which a compound leaf is formed. The petioles, or leafstalks, either bend 
upwards or downwards, so that the flattened surface or limb of the leaf is elevated 
or depressed. There are about a dozen modifications in the manner in which the 
leaves are inclined to the stalks on which they grow ; some raise their leaflets so 
that their upper surfaces are brought into contact ; and others depress them so that 
the under surfaces meet together. This phenomenon is best exhibited by various 
species of the two natural orders ; the Leguminosce (which includes both the pea- 
flowering plants, as clover, &c., and the Acacias and Mimosas, &c., which have 
regular flowers), and the Occalidece. These phenomena depend upon a special 
physiological law, subject in some degree to the stimulating effects of hght and 
heat which elicit and control them, but which are not themselves the primary 
causes of these eff'ects. When the sensitive plants are confined in a dark room, 
their leaflets periodically fold and open as usual, except that the periods are some- 
what lengthened ; on the other hand, when they are exposed to a continued light, 
these periods are shortened. When exposed to strong lamphght by night, and 
excluded from all light by day, their periods of sleep become extremely irregular 
for a time ; but, in the end, the specimens generally close their leaves during the 
day, and unfold them at night - 
The alternate opening and closing of flowers is a similar function to that of the 
sleep of leaves. The time of day in which flowers close is very difl'erent for 
different species, and even differs for that period during which the leaves are asleep 
on the very same plant. Bertholet mentions an Acacia in the garden at Arotava 
in Teneriffe, whose leaflets closed at sunset and unfolded at sunrise, whilst its 
flowers closed at sunrise and expanded at sunset. — Henslow's Botany, in Dr, 
Lardners EncyclopcBdia. 
NEW AND RARE PLANTS, 
FIGURED IN THE LEADING BOTANICAL PERIODICALS FOR OCTOBER. 
CLASS I PLANTS WITH TWO COTYLEDONS (DICOTYLEDONE^). 
THE CAMPANULA TRIBE (cAxMPANULACE^E). 
Campanula Portenschlagiana. Dalmatian Wall Campanula. A pretty 
little herbaceous species, hardy in the milder parts of Great Britain, it however 
succeeds best if kept in a greenhouse in winter. It is a native of the walls and 
rocks in Dalmatia, whence it was introduced by the Hon. W. F. Strangways. Bot. 
Reg. 1995. 
