Posted
on October 2, 2014
Today's
famous birthday was a botanist extraordinaire!
You
probably know that botanists study plants.
You
could look at plants as living things that don't move around or make
sounds or, really, do much of anything – or you could look at
plants as incredible living factories that convert solar energy, gas,
and water into food. You could also look at plants as living things
that DO move, actually...
Julius
von Sachs, born in Prussia (Germany) on this date in 1832, advanced
the study of plant physiology in many different arenas, but one area
he added a lot to was the study of the way that plants move in
response to gravity, light, and water.
These
plant responses are called tropisms.
Geotropism
Roots
grow downward, and stems and shoots and tree trunks grow upward. That
seems so obvious, but notice what happens when you lay a potted plant
on its side:
The
roots bend in order to continue to grow downward, toward the
gravitation pull of the Earth. (This tropism is sometimes called
gravitropism.)
This is called positive geotropism.
And
the stem bends in order to continue to grow upward, away from the
gravitational pull of the Earth. This is called negative geotropism.
Phototropism
You
have probably noticed many times that plants tend to bend toward
light. Because the sun moves through the sky during the day, outdoor
plants often make cycles, always following the sun as it arcs from
east to west each day.
(This
tropism is sometimes called heliotropism.
However, plants also bend toward artificial lights; with helio-
meaning sun
and photo-
meaning light,
the latter seems more correct.)
Hydrotropism
Another
tropism is the bending toward a water source.
Here
are some videos about tropisms and plant movements:
Also
on this date:
Great
Books Week
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ahead:
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