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Sunday, March 20, 2016

Plant power

We usually notice the power of nature in big, dramatic phenomena—waterfalls, ocean tides, shifting tectonic plates. But very small plants do things that I think are just as awe-inspiring.

    At this time of year, I’m surrounded by evidence of the amazing strength of growing plant tissue. For example, there’s the sight of growing tips of new spring sprouts, so soft and tender to our touch, pushing their way through rigid barriers like the oak leaves lying on my garden soil.

These daffodil tips grew through tough oak leaves

    How can this be? The dried oak leaves are quite resistant to tearing or punching through. But we know that growing plants are powerful enough to split rocks.

This fern widens fissures in the rock

    On Wayne’s Word, an online natural history textbook created by botanist Wayne P. Armstrong, I read:

"One of the main factors that initiates the rock-splitting scenario is imbibition--the remarkable process by which water molecules move into a porous, colloidal material and cause it to swell." Wayne explains that electrical charges carried by the oxygen and hydrogen atoms in water are attracted to charged components of large molecules inside plant cells, such as cellulose, starch and lignin (the polymer that strengthens and hardens plant cell walls): “Like tiny magnets, the water molecules permeate these polymers, adhering to the charged surfaces as well as cohering to the positive and negative ends of adjacent water molecules. This influx of water molecules and chemical bonding . . . causes the cell wall and its contents to swell several times its original size.”

    Wayne goes on to explain that water swelling a seed before germination can exert hundreds of pounds of pressure per square inch in order to split the seed coat of a hard nut like a walnut. So pushing through an oak leaf that’s frozen in place may be little challenge for a growing crocus or daffodil tip.

    It’s interesting to think about the power that small and unassuming plants can exert.  An acorn germinating in a crevice in a rock can ultimately split the rock.  Roots not only buckle sidewalks, they push their way into the joints in pipes—as I was reminded again last spring when sewer water backed up into our basement drains.

Norway maple roots defeating granite curb on my block

    In case we gardeners get the idea that we run the show, the slow power of those little shoots and roots reminds us that bigger forces are at work, gradually and inexorably. You don’t have to go to the seashore or the mountains to be awed by nature’s power.

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