Summary.The present status of our knowledge of the form and structure of the plant body in the genusUtricularia(incl.BiovulariaandPofypompholyx), apart from the formal morphological point of view, is briefly presented.The account embraces (a) the period of embryological development, during which anatomical‐nutritional relations are prominent; a very peculiar feature is the abstriction of the root pole of the embryo by the endosperm; (b) the form of the rootless definitive embryo; and (c) its behaviour during germination, of which there are several types.Then follow descriptions of the various biological forms of the so‐called leaf, stolon, tubers and resting buds.The various forms of the trap (bladder) are described. While all have the same fundamental structure, the general form may be extremely simple in bearing no appendages, or may be equally complex in having numerous appendages of various kinds. The biological meaning of these is problematical.The entrance mechanism of the trap is analysed and its mode of operation is shown. It is composed of two valves, the larger being the door, and the smaller being the velum, which overlies the edge of the larger. When the trap is set the door edge rests against an opposing surface of a ridge, the threshold, which impedes its swinging inwards, and in this position the door and the velum are mutually so adjusted as to be watertight. The setting of the trap is achieved by diffusion of water from its interior, a condition of unstable equilibrium being set up. The adjustment of the trap to this condition consists in the partial collapse of its side walls. Springing of the trap consists in disturbance of some sort of release mechanism consisting of bristles, larger or shorter trichomes, which thus distort the door, allowing the higher outer water pressure to swing it in. The entering water current carries in the prey if suitably placed.Although ali the traps known are alike in principle of action, there is a considerable diversity of form and structure. The differences lie in the relative positions of the threshold and valves, and in the relative quantitative importance of their mutual thrusts. Such differences are expressed in an extended variety of form of every p