CARNIVOROUS PLANTS. 
361 
of a, digestible substance, and have no power of motion. The 
faculty of detention lies in the elasticity of the tissue of the 
leaf itself. On the upper surface are six strong hairs or bristles 
which display extraordinary sensitiveness, conveying to the rest 
of the leaf an irritation when touched, which causes the leaf 
suddenly to fold up, the sharp serrations or spikes with which 
the margin is covered closing upon one another, and interlocking 
like the teeth of a rat-trap. The glands, which are in this in- 
stance true epidermal structures, secrete an almost colourless, 
slightly mucilaginous, strongly acid fluid, but only when excited 
by the presence of nitrogenous matter, which they have the 
power of absorbing. This secretion, the formation of which is 
seen, from what has been said, to be altogether independent of 
the mechanical irritation of the leaves, appears, from Mr. Dar- 
win’s experiments, to have a distinct power of digestion. The 
most remarkable fact connected with Dioncect is in the differ- 
ence in the behaviour of the leaves after closing, according to 
whether a digestible substance, an indigestible substance, or 
nothing at all, has been captured. In the two latter cases the 
leaves reopen in less than twenty-four hours, and are then again 
at once sensitive to renewed impact. In the first case, on the 
contrary, they remain closely shut up for many days, and after 
re-expanding are torpid, and never act again, or only after a 
very considerable interval of time. Moreover, when the leaf is 
made to close over an insect or other body containing soluble 
nitrogenous matter, the two lobes, instead of remaining concave, 
as they otherwise do, enclosing a small cavity, slowly press close 
together throughout the whole of the blade with very consider- 
able force, and offer very great resistance to any attempt to 
force them apart. Mr. Darwin draws some very interesting 
conclusions from these facts ; showing how this arrangement 
allows small insects to escape before they are crushed and thus 
yield up their nutrient juices, while larger insects are hope- 
lessly entrapped; the digestive process being therefore only 
brought into play when a considerable quantity of nutriment 
is at the command of the leaf. Dr. Burdon Sanderson has made 
the additional extremely curious observation * on the Venus’s 
fly-trap, that a normal electrical current traverses the blade and 
the foot-stalk of the leaf, while the current is reversed when the 
leaves are irritated or the foot-stalk cut. The phenomena there- 
fore present a most remarkable analogy to those which occur in 
the muscles of animals when contracted ; although there does 
not appear to be anything whatever in the Dioncea which can 
in any way be compared to the nervous tissue of animals. 
* " Proceedings Eoyal Society,” vol. xxi. p. 495; and “Nature,” 1874, 
pp. 105 and 127, 
