In the Garden:
Middle South
May, 2004
Regional Report

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1417

To protect their precious pollen from dew, my 'Kiss Golden Flame' gazanias close up at night and reopen in the morning.

Mysterious Movements

Back in the 3rd Century B.C., Theophrastes noticed that plants don't just sit there. They move. Tulips close up in the cool of the night, and four-o'clocks open late in the afternoon. Watching the way some plants fold and unfold their flowers and leaves, he concluded that plants have souls. Perhaps he was right! I share Theo's fascination with such things, which makes the garden more interesting at any time of day.

Nastic Actions
Scientists have a word for the opening and closing of blossoms and the folding and unfolding of leaves: nastic movements. Daylilies do it, as do morning glories, portulaca, black-eyed Susan vine, and lots of other flowers. But how? And why? I never thought of flower petals as having muscles, but it turns out they do. Special "motor" cells at the base of these flowers are able to contract and expand, which causes the petals to move. Plants that fold their leaves at night, such as mimosa and prayer plant, do it by working motor cells in the petioles -- the little stems at the base of each leaf. In these plants, moisture changes in the petiole and central leaf vein work like a hydraulic hinge.

But is it really necessary for my gazanias to fold up each night? Apparently they think so, because flowers are interested in only one thing: reproduction. The folded petals keep the pollen dry so it will be ready for transport the next day, as soon as pollen-seeking insects hit the air. My nicotiana closes up shop during the day so its precious cache of fragrant nectar will be ready and waiting for hummingbird moths and other night fliers, which do a superior job of fertilizing its flowers.

The triggers for nastic movements can be light, temperature, humidity, touch, or a combination of factors. The plants know what they're doing, and now you do, too.


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