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| A, leaf of Butterwort (Pinguicula vulgaris) with left margin inflected over a row of small flies. (After Darwin.) B, glands from surface of leaf by which the sticky liquid is secreted and by means of which the products of digestion are absorbed. |
BUTTERWORT, the popular name of a small insectivorous plant, Pinguicula vulgaris, which grows in wet, boggy land. It is a herb with a rosette of fleshy, oblong leaves, 1 to 3 in. long, appressed to the ground, of a pale colour and with a sticky surface. Small insects settle on the leaves and are caught in the viscid excretion. This, like the excretion of the sundew and other insectivorous plants, contains a digestive ferment (or enzyme) which renders the nitrogenous substances of the body of the insect soluble, and capable of absorption by the leaf. In this way the plant obtains nitrogenous food by means of its leaves. The leaves bear two sets of glands, the larger borne on usually unicellular pedicels, the smaller almost sessile (fig. B). When a fly is captured, the viscid excretion becomes strongly acid and the naturally incurved margins of the leaf curve still further inwards, rendering contact between the insect and the leaf-surface more complete. The plant is widely distributed in the north temperate zone, extending into the arctic zone.