butterwort defined in 1912 yearbutterwort - Butterwort (Pinguicula vulgaris);
butterwort - Our ideas of the usual happy relations between plants and insects receive a rude shock when we learn the truth about the Butterwort. While its flowers, by their colour, shape and the honey they contain, are inviting insect visitors in the ordinary way to carry their pollen from flower to flower, the leaves are setting themselves deliberately to catch, kill and eat any small flies that may be so unwary as to fall into their trap.
The Butterwort is a little plant. In the marshy uplands of Wales, Yorkshire and the Lake District it is chiefly to be found, a rosette of leaves lying on the ground, from the centre of which the flowers rise singly on stalks three to five inches high. The leaves are a pale, shining green, the flowers blue-purple of irregular shape. It is unmistakable.
The leaves far more than the flowers are the main point of interest. They are spoon-shaped, and covered with a sticky fluid, and usually have the bodies of little flies adhering to them, but though our forefathers recognised both the structure and the presence of the flies, and called the plant Butter-wort in English parlance, and Pinguicula (Pinguis, fat) for its botanical name, they did not realise the connection between them until Charles Darwin pointed it out. All over the face of the leaf are two kinds of small glands, one of which can be clearly seen with the naked eye, though it needs a lens to show us that it has a rounded top and a stalk, so that it looks precisely like a small mushroom; the other is smaller and minutely wart-like.
An ordinary Butterwort will have no fewer than half a million of these glands on its leaf-rosette. We do not yet know in what way the functions of the two sets of glands differ, but we know their joint work; they secrete two kinds of liquids, one colourless and very thick and sticky, the other an acid digestive liquid, which has been proved to be identically the same as the gastric juices in our own stomach.
Imagine a fly settling, say, near the margin of a leaf. Directly its legs touch the gummy surface it is caught as on a fly-paper. Naturally it struggles to escape, but the only result is that more sticky liquid is poured out and it is glued down still more firmly, while the edge of the leaf curls very slowly over so that, if a small fly, it is carried into the centre of the leaf, and, if a large one, it is pushed there. Meanwhile the digestive liquid is also oozing out, and soon the fly is dead, and in twenty-four hours there is nothing left but its claws, wings and scales. All the nutritive portions have been absorbed by the leaf. When a fly was placed in the very centre of the leaf as an experiment it was found that both margins began to curl over towards it and they reached it in four hours and twenty minutes. The object of this curling-up is twofold; it brings more glands into actual contact with the victim's surface, and it also prevents any of the secretions from overflowing. Eventually they are all re-absorbed into the leaf-tissue, enriched by the flesh they have dissolved. It is an interesting point that it is only when the substance that falls on the leaves is such that they can digest it that they curl over and attempt the process. Small stones, particles of coal, and the like are completely ignored, but insects small pieces of flesh, clotted blood, even cartilage, as well as seeds (if their envelopes be not too tough) and pollen wafted by the wind at once set the secretive and digestive processes in motion.
It can readily be understood, then, that the Butterwort leaves can act in the same way as rennet from a calf's stomach, and though country folk may not have appreciated the scientific aspect of the question they have the practical, and Butterwort leaves, when plentiful, have long been used by dairy farmers to curdle milk. Linnæus, a hundred and fifty years ago, wrote of a favourite Scandinavian dish called satmiolk, or tätmiölk, which is a mass of thick, tough curds produced by pouring milk warm from the cow over Butterwort leaves. The Laplanders make it with reindeer milk, and allow it to stand a day or two until it becomes sour and very thick. Fresh tätmiölkcan be produced by merely adding some of the old curd to new milk, a point worthy of special emphasis, since we see that the substance produced by the plant is identical in action to other ferments. Village healing lore applies the leaves to broken braises, and the Alpine shepherds place them on any sore on the udders of their cows, these remedies being particularly interesting, "inasmuch as the curative effect on the sores is to be explained by the antiseptic action of the secretion of the leaves in question, and a method of healing used empirically two centuries ago thus finds confirmation and a scientific explanation at the present day." (Kerner.)
The flowers, though dwarfed in interest by the leaves, are nevertheless very noteworthy. Both calyx and corolla respectively are united, the corolla being much larger than the calyx and forming two lips. The flower stalk curves so that the flower hangs sideways, its open mouth outwards. The upper lip is made up of two smaller petals; the lower of three large ones, in the centre of which there is a white patch marked by purple lines and densely clothed with soft hairs; the rest of the blossom is smooth. The lines point to where a thick straight spur runs back from the petals, and lies just under the flower stalk. Honey is stored in it. Attached at the back of the corolla, just above the entrance to the spur cavern, are two stamens, and above them again is an egg-shaped ovary with a thick stigma, a branch of which hangs down right in front of the stamens. A bee approaches - the flower is specially adapted to bees - and settles on the broad lower lip, finding firm foothold on the hairy patch, and he thrusts his head, dusty with pollen from a neighbouring blossom, into the flower. As he inserts his proboscis down the spur he rubs his head on the branch of the stigma that covers the stamens, and it is ready to receive the pollen for its fertilisation. But directly he passes the stigma he is in contact with stamens hiding just behind and they promptly discharge their pollen on him, so that in one moment the bee gives up some he brought with him and gains other to take away. As the bee retreats he pushes back the stigma to its original position.
Suppose no bee happens to favour the flower with its presence, still seed is not denied to it, for then the curtain-like stigma curls round and itself touches the stamens and receives pollen from them directly.
The fruit is a small capsule held upright and enclosed in the calyx from which it projects. In fine weather it opens widely at the top so that the seeds can escape, but should rain fall, this opening closes and keeps the seeds within dry, to re-open when the weather is more propitious.
The Butterwort is often known as the "Bog Violet," from its purple flowers. It is also called (most unjustly) "Rot Grass," from the idea that it causes rot in sheep, the truth being that the only connection between the two is that both sheep and plant may be in the same boggy meadow, which is too damp for the animal though not for the plant. "Yorkshire Sanicle " is another old name.
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