840 
SPONTANEOUS MOVEMENTS IN PLANTS. 
jerking movements; now stopping for some time, then 
moving briskly, always resting for a while in some part of 
their course, and starting again without apparent cause, 
“ seemingly of their own will," as Prof. Asa Gray remarks. 
The movement is not simply up and down, but the end of 
the moving leaflet sweeps more or less of a circuit. It is not 
set in motion by a touch, but begins, goes on, and stops, of 
itself. 
An exceedingly remarkable instance of sensitiveness occurs 
in the case of the “Venus's Fly-trap 5 ' of North Carolina, 
Dionoea muscipula. In this plant the mid-rib of each leaf 
serves as a kind of hinge. When the inside of the blade of 
the leaf, or the fine bristles which grow on its surface, are 
touched by any foreign substance, the hinge suddenly closes, 
and if the intruding substance be a fly or other small object, 
it is immediately imprisoned as represented in the figure, the 
teeth on the margin of the leaf closing firmly upon one 
another like a steel trap, the sides of the trap then flatten 
down and press firmly upon the victim, and it now requires 
a very considerable force to open the trap. If nothing is 
caught the trap presently reopens of itself, and is ready for 
another attempt. With regard to the object of this strange 
proceeding, there can be no doubt that the insect is retained 
until the softer parts of the body are completely dissolved in 
the thick mucous fluid which is exuded by the leaves; and 
Professor Asa Gray considers that the evidence is nearly 
complete that the animal matter is actually absorbed in the 
leaf itself. It is even stated that pieces of raw beef are di¬ 
gested by the leaf in the same manner! Seeing, however, 
that it is now generally admitted by physiologists that even 
pure water is not absorbed through the pores of leaves, which 
serve only for the exhalation of vapour, this explanation is 
very hard of belief. The “ pitchers " of the Nepenthes , or pit¬ 
cher-plant, act also as fly-traps, large numbers of insects being 
enticed into them by the fluid they secrete, and are then un¬ 
able to extricate themselves. 
The sensitiveness of the leaves of plants is but an excessive 
development of the phenomenon known as the Sleep of 
Plants. In the case of the Sensitive Plant the position assumed 
by the leaf and leaflets in the night is the same as that which 
they assume when disturbed in the day-time; and with many 
other plants, such as the clover and the Robinia or “acacia 55 
tree, the change in the position of the leaflets, morning and 
evening, is a familiar fact. The Sleep of Plants extends also 
to the flowers, many plants opening their flowers only at 
particular times of the day. Thus, the major convolvulus of 
