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By Root 515 0

they expand instantaneously while they engulf their prey. This was in England, while in India, at about the same time, another naturalist made the same discovery in a different way. While distributing for study by his class specimens of a Utricularia with exceptionally large bladders, T Ekambaram (1916) heard crackling sounds, somewhat like the ticking of a watch, each time he lifted a spray from the water. He traced the sounds to the bladders, which expanded and sucked in air as they were drawn through the pond's surface film, and he recognized that this almost explosive dilatation was their method of capturing prey. As a bladder emerges into the air, the water's contracting surface film apparently moves

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the trigger bristles and springs the trap, which draws in air and becomes inactive.

Finally, in 1925, Professor R. W. Hegner of Johns Hopkins University, while studying the fate of minute protozoa trapped in the bladders, incidentally noticed that they capture animalcules by suction. While I was a graduate student in botany at the same university, Hegner interested me in the history of the bladderwort. I found that the expansion of the bladders was quite obviousafter one knew what to look for (Skutch 1928). Nevertheless, without this initiation, the bladderwort's secret was so carefully guarded that it escaped Charles Darwin himself, his botanist son Francis, and other competent observersall of which makes an interesting minor episode in the history of science that seemed worthy of recounting here.

The independent discovery by four people in as many countries of how victims are sucked into the bladderwort's green charnels raised other questions: How does the bladder's rapid expansion come about? What is its mechanism? This problem was tackled with fruitful results by two German botanists, Edmund M. Merl (1922) and A. F. Czaja (1922), who made it clear that the release of the set Utricularia trap is not, like the closure of a Venus's-flytrap leaf or the flexure of sundew tentacles, effected by a sensitive motor organ but is more mechanical, like springing a mouse trap. Later, Francis E. Lloyd (1942), an English botanist resident in the United States and Canada, called attention to a final detail, the delicate membrane that seals the trap door. The elucidation of the bladderwort's activity has been a thoroughly international endeavor, as all good science should be.

To understand the operation of a Utricularia bladder, let us choose one that has just expanded and follow its subsequent behavior. After the entry of the first victim, the valve, helped by its outward convexity, springs forward against the sillmuch as a piece of flexible cardboard, bent into half a cylinder and indented by a finger at its lower edge, regains its convexity the instant the finger is removed. The four-armed hairs that cover the bladder's inner wall continue to absorb from the cavity water that is excreted to the exterior, probably chiefly by the sessile glands on the outside.

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Since water cannot enter the bladder through the tightly sealed orifice, as its volume is reduced the side walls are slowly forced together by the pressure of the atmosphere and the overlying pond water, just as our cheeks are pressed against our teeth when we close our lips tightly and suck air from our mouth. The indrawn walls are elastic and tend to expand, which would draw in the valve and admit more water if the outward bulge of the valve, pinched by the incurved walls, did not resist the excess pressure of the medium. Viewed from above, the bladder has become much thinner than when newly sprung.

If now, fifteen to thirty minutes after the snare made its last capture, a small swimming creature impinges against the valve or its bristles, the unstable equilibrium is upset. The seal is broken; the strained walls spring outward, as through the orifice they draw in a current of water that carries into the trap the ill-omened creature that sprang it. The whole process is so swift that it escapes the notice of excellent