October 2 – Happy Birthday, Julius von Sachs

nPostednon October 2, 2014

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Today’snfamous birthday was a botanist extraordinaire!

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nYounprobably know that botanists study plants. n

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nYouncould look at plants as living things that don’t move around or makensounds or, really, do much of anything – or you could look atnplants as incredible living factories that convert solar energy, gas,nand water into food. You could also look at plants as living thingsnthat DO move, actually… n

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nJuliusnvon Sachs, born in Prussia (Germany) on this date in 1832, advancednthe study of plant physiology in many different arenas, but one areanhe added a lot to was the study of the way that plants move innresponse to gravity, light, and water.

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nThesenplant responses are called tropisms.nn

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nGeotropism

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nRootsngrow downward, and stems and shoots and tree trunks grow upward. Thatnseems so obvious, but notice what happens when you lay a potted plantnon its side:

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nThenroots bend in order to continue to grow downward, toward thengravitation pull of the Earth. (This tropism is sometimes calledngravitropism.)nThis is called positive geotropism.

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nAndnthe stem bends in order to continue to grow upward, away from thengravitational pull of the Earth. This is called negative geotropism.

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nPhototropism

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Younhave probably noticed many times that plants tend to bend towardnlight. Because the sun moves through the sky during the day, outdoornplants often make cycles, always following the sun as it arcs fromneast to west each day. n

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n(Thisntropism is sometimes called heliotropism.nHowever, plants also bend toward artificial lights; with helio-nmeaning sunnand photo-nmeaning light,nthe latter seems more correct.)

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nHydrotropism