The water smells abominably, and contains the bodies of dead insects, and rubbish of all kinds (see also p. [298]). The remnants of these drowned insects are probably of use, because any valuable nitrogenous or other material may be absorbed with the water by the plant and help to nourish it, but in such a rough contrivance as this there is nothing comparable to the Side-saddle plant, Pitcher plant, and others.
The former, Sarracenia (or Side-saddle plant), is a common and rather widespread North American plant, which is especially abundant in Florida. It is cultivated in most botanical gardens, but can only be grown in greenhouses. The leaves are about six inches to a foot long, and are hollow, funnel-shaped tubes with a short, flat wing along one edge. They may be an inch or two in diameter at the top or wider end, where there is also a sort of half-open lid which keeps rain from getting into the inside of the leaf. The colour of these tube-like or vase-like leaves varies. It is often variegated with brown, red, and yellow, and is conspicuous enough even at a distance. Thus insects fly to these vases and alight on the little cap or lid, where they find honey and enjoy themselves. Other insects crawl up along the rim or wing of the vase, finding honey here and there along their road. Having got to the lid, the insect, being of an inquiring or inquisitive disposition, will look inside the tube and endeavour to find more honey therein.
It reaches the rim of the vase and finds that there is honey inside; it can easily crawl down, and fails to notice that the inside of the vase is lined with long stiff points which all point downwards. These points or hairs do not at all interfere with its passage down, and it proceeds to the honey which forms a smooth, slippery coating. Then, after greedily absorbing the honey, it tries to get out again. But that is quite a different matter. Each one of these points or hairs is facing it, and the whole inside is smooth and slippery. It struggles, slips, and falls into a pool of water which fills the lower part of the vase. That is what the plant has developed these pitchers for. The body of the insect after a time decays away, and only its empty shell remains. An extraordinary number of insects are caught by these Sarracenia vases. Sometimes in one which is only ten inches long, three or four inches will be full of the corpses of blackbeetles and other drowned insects, and it is said that birds occasionally visit these vases in order to pick them out. There is probably some sort of secretion in the water. "A centipede 1-2/3 inches long having fallen into a vase of Sarracenia purpurea in the night was found only half-immersed in the water. The upper half of the creature projected above the liquid, and made violent attempts to escape; but the lower part had not only become motionless, but had turned white from the effect of the surrounding liquid; it appeared to be macerated, and exhibited alterations which are not produced in so short a time in centipedes immersed in ordinary rainwater."[148]
In some Sarracenias the vase is brought up into a sort of hood or dome with the entrance at one side and below. There are thin patches on this dome or cupola, and small insects, attracted by the light which comes through these bare places, remain dashing themselves against them or crawling over them just as flies do on a window-pane, until they become tired and fall down into the water below.
There is something horrible in the cold and careful way in which this plant arranges its baits for "confiding insects. The latter are fed with honey, even on the very border of the assassin's den, but after this farewell revel they generally slip upon the smooth edge, and are hurled, like lost souls, down into the abyss."[149]
In another plant, the Pitcher Plant (Nepenthes, so called from the drug which produces the sleep of death), we find an even more beautifully arranged pitcher which acts in very much the same way. It is, however, only the end of a rather long leaf, or rather of its midrib, that is turned up to act as a pitcher. There are similar stiff hairs pointing downwards, and honey is plentifully secreted. But, in Nepenthes, there is also a distinct secretion which digests the bodies of the drowning insects. The ferment resembles the active principle of the gastric and pancreatic juices of the human body, and, as acids are also present, the insect's body becomes changed into nutritious juices which readily diffuse into the plant.[150] Dr. Macfarlane found that when the pitchers were stimulated by being given insects, the liquid inside them could digest fibrin to jelly in from three-quarters to one hour's time.[151] But certain insects have somehow managed to educate their larvæ to resist the gastric juices of Nepenthes.
Near Fort Dauphin, in Madagascar, I found great quantities of Nepenthes madagascariensis. Almost every pitcher was one-third to two-thirds full of corpses, but in some of them large, fat, white maggots, of a very unprepossessing appearance, were quite alive and apparently thriving. These must have been the larvæ of a blowfly similar to that which has been mentioned by others as inhabiting Sarracenia. At the same place a white spider was very often to be seen. Its web was spun across the mouth of a pitcher, and its body was quite invisible against the bleached remains inside.
It had suited its colour to the corpses within, in order that it might steal from the Nepenthes the due reward of all its ingenious contrivances!
A totally different arrangement is found in an inconspicuous and ugly little marsh and ditch plant called Utricularia or Bladderwort. It is very difficult to see, for unless it happens to be in flower it is entirely submerged in the water. The flowers, which are purple, are conspicuous and easily seen even at a distance. On these submerged leaves there are hundreds of small bladders. They are about the size of a pea, and are most ingeniously contrived to catch small water-animalcula. The general idea of the bladderwort is exactly that of the eel-pots so common in some parts of the Thames. There is a small flap which acts as a trapdoor. Small creatures probably take refuge in the bladders when pursued by the larger water-fleas, etc., for it must seem to them to be a safe and secure retreat.
But once within the door, they are imprisoned and cannot find their way out again. They perish inside and their bodies are digested by the plant; on the inside of the bladder there are gland hairs which also secrete a digestive fluid.