Science: Why . . .?

Scientific solutions from last week’s University of Chicago meetings:

> Why do plants bloom faster when their flowers are picked? The dominant bud, explained Plant Physiologist John William Mitchell of the U.S. Department of Agriculture, apparently produces a hormone which inhibits growth of the other buds on the same stem. If it is snipped off, the uninhibited buds can burst into bloom.

> Why are there evergreens in the South, oaks in the North? Botanist William Spinner Cooper of the University of Minnesota studied fossil tree pollens in peat, concluded that “in America the climate following the glacial epoch was warm and dry, with a return to a cooler moister climate during the last few thousand years.” Thus the cone-bearing evergreens of the Southern U.S. are relics of the glacial invasion (which halted at the Ohio River), and the North’s oaks and other hardwoods are relics of the warm postglacial period.

> “Why is rubber so elastic?” asked Physicist Eugene Guth of Notre Dame. “This is a problem which has baffled scientists for a long time and it was not until recently that an explanation could be offered. . . . A property of rubber, not well known, can easily be demonstrated with a rubber band. Stretch it quickly against the upper lip. It feels warm. Conversely, if it is kept stretched for a little while, then released, it feels cool. This generation of heat by the band . . . proves that the relation between the heat of the rubber and its compression is similar to that of gas compressed by a piston in a vessel. If the gas is kept at a constant volume . . . the pressure on the piston will increase proportionately with the temperature.”

On the mechanism of rubber elasticity. Physicist Guth said: “The molecules of rubber are like long flexible strings. . . . If one throws a flexible string into the air, it will land in a curved, coiled-up form, rather than a straight form. Similarly, in an unstretched rubber band, the rubber molecules will be coiled up. Stretching the rubber actually stretches its long flexible molecules from the curved to the straight form.”