Try turning a growing plant on end, and a funny thing happens.
It will right itself, twisting and contorting so its leaves
project skyward and its roots extend down toward the center of
the Earth. Logic would dictate that plants solve the problem of
which way to grow by sensing gravity — but how did scientists
ever prove that this is correct? Over on NPR, Robert Krulwich
recounts the story of scientist Thomas Knight and the first
experiment to demonstrates that plants do, in fact, sense
gravity: He attached a bunch of plant seedlings onto a disc
(think of a 78 rpm record made of wood). The plate was then
turned by a water wheel powered by a local stream, "at a
nauseating speed of 150 revolutions per minute for several
days." If you've ever been at amusement park in a spinning tea
cup, you know that because of centrifugal force you get pushed
away from the center of the spinning object toward the outside.
Knight wondered, would the plants respond to the centrifugal
pull of gravity and point their roots to the