THE BLADDERWORT
We have no wonderful pitcher-plants in our own country, except those which are grown in hot-houses as curiosities; but there is a modest-looking little plant called the "Bladderwort" living in mountain tarns in Scotland, and in little pools on the moors and marshes in many parts of England, that has just as clever an insect trap as any of the fine and gaily-colored plant-ogres of foreign lands.
During the summer months you may discover the whereabouts of the bladderwort by the bright golden flowers, that look rather like orchids, which rise above the water on slender flower-stalks, springing from the floating stem of this strange little plant. But when its flowering time is over it is not so readily seen, for its leaves are very small, and always float in the water below the surface of the pool.
Like many other water plants the bladderwort has no roots. It has simply a long, straggling stem, which is always growing at one end and dying away at the other. The leaves are all cut up into fine fringes, which wave up and down in the water, trying to catch all the atoms of dissolved carbonic acid gas they can find around them in the pool.
But the bladderwort is not satisfied with the nourishment it can obtain from the water in this way. It is not content unless it has a constant supply of fresh animal food. So all aling its stems the hungry plant has hundreds of little swellings called "bladders," which are nothing more or less than traps to catch its dinner.
These bladders are very tiny. They are usually no more than a tenth of an inch long. But they are quite big enough to trap and hold many of the wee water-creatures that are always to be found in abundance in every pool where the bladderwort grows. For every little moorland pool and every little mountain tarn is the home of countless numbers of tiny water-folk the larvae of gnats and midges, queer sprightly little water-fleas, and all sorts of odd wee creatures almost too small to be seen without the aid of a magnifying glass.
These things lead a most perilous existence. Not only are they gobbled up wholesale by the larger inhabitants of the pools, but many of them, particularly the little water-fleas, which are always bobbing and jerking about in the water, spinning round and round like tee-to-tums and clutching each other with their funny long feelers, are caught in the cunning little traps of the bladderwort.
The bladders are really leaves that have become altered to enable the plant to catch its food. They are little hollow chambers with pretty pale-green, half transparent walls, and are filled with water and bubbles of air. Each bladder is set on a slender stalk, and is provided with a little trap-door, which opens inwards to allow little water creatures to enter easily. Round the doorway is a number of long, stiff bristles, projecting outwards to keep off the larger inhabitants of the pool, which might injure the trap by blundering against it.
Between these bristles the water-fleas can slip quite easily, and no doubt they often take shelter among them when pursued by an enemy. There, either in a panic, or just out of idle curiosity to see what is beyond, they butt their heads against the little trap door, which swings inwards to let them pass and closes with a snap behind them.
But the water-fleas find they have made a great mistake in heedlessly entering this convenient little green-house. It was easy enough to slip in, but try as they may they cannot get out again. Most of the little creatures try hard to escape, but their efforts are all in vain. It is no use butting against an outer ridge which projects all round the mouth of the bladder, and no amount of pushing can force the door outwards. Every now and again, indeed, it swings inwards to allow another little victim to pass into the trap, but it shuts instantly again behind it, as if with a spring, before the prisoners within have time to pop out.
For a day or two they may live inside the bladder, but the trap soon becomes uncomfortably crowded with all the deluded little water-folk that push their way so gaily past the treacherous swing door; so one after another they all die of starvation or suffocation. They then decay, and the water in which their bodies are partly dissolved is sucked in through hundreds of little mouths in the wall of the bladder, and used to strengthen the plant.
No fewer than twenty-four water-fleas, besides several tiny worms, gnat larvae and other small insects of the kind, have been found in one of these traps, so the bladderwort certainly seems to need a good deal of food. But this is partly because in the summer days, when water-fleas are plentiful, the bladderwort is busy storing up provision for the winter.
When summer is over a thick tuft of new leaves is formed at one end of the stem of this curious plant, while all the rest of the stem and leaves, and all the bladders die away. Then the tuft of leaves sinks to the bottom of the pool and passes the winter resting in the mud. When spring comes round again the bladderwort rises once more to the surface of the water, forms a new set of bladders and starts catching water-fleas again.
at one time people used to think the bladders were floats to keep the plants floating near the surface of the water, but this was a great mistake, for, of course, water-plants do not need floats to keep them from sinking. Other water-plants have not any bladders at all; yet they float just as easily as the bladderwort.