the _keel_ or pair of lower petals. Pressed down by its weight, these open, often with a sudden movement like bursting, and dust the insect with pollen. Compare also the flowers of the Snapdragons (_Antirrhinum_) and Toadflaxes (_Linaria_), in which the upper and lower lips of the corolla meet like a closed mouth, which can be forced open only by a strong insect like a bee, and is safe from predatory visits of smaller fry (Fig. 18). In the Sages (_Salvia_) the corolla is tubular at the base; there is a large lobed lip on which visiting insects alight, and a hooded roof above arching over the stamens and pistil, which are placed close against it, overhanging the entrance to the corolla-tube, at the base of which the nectar is stored. The stamens, only two of which are developed, have each a hinge near the top, the part above the hinge being like a curved rod supported near its middle. These two curved rods stand normally in a vertical position, so that their lower ends partly block the entrance to the tube; the pollen is borne at their upper ends. Should a bee insert its head down the tube in search of nectar, it pushes the lower ends of the hinged rods upwards, with the result that their upper ends swing downward against the bee’s back, dusting it with pollen just at that part of its body which, if the bee should visit a rather older flower, would come in contact with the stigma, the slender stalk of which (the _style_) increases in length during the period of flowering, and is in consequence the more liable to be encountered. [Illustration: FIG. 18.--FLOWER AND FRUIT OF LINARIA PURPUREA. 2/1.]