outside in the garden

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Astragene, with thanks to Garden web

Saturday, July 13, 2002

Sky lilies
We planted nasturtiums this year in several locations. The best of them is under the shrubbery at the mouth of the driveway, a spot that gets sunlight only in the early morning, as it slants in from across the street where I live. The rest of the day, the shrubs and tall trees shade it completely.

The little fellows are up, with their nice rounded leaves, like little puffed-out chests, facing east. My daughter calls nasturtiums sky lillies because they are so extremely photo-sensitive. As the sun progresses across the sky, the nasturtiums turn with it; the result is twisted little stems.

The mechanism of plants "turning toward the light," I was told years ago, is certain growth hormones are activated in the shade. The shady side of the plant thus grows faster, giving the effect of the plant bending toward the light.

Mechanically, this is the same principal used in electrical auto-off and -on switches, which respond to the heat generated by an electrical connection. A little metal piece that makes a complete circuit when closed, thus turning the light on, is made with two different metals back-to-back,* one of which warms and expands at a faster rate than the other, thus bending the piece to open the circuit. Once the power is off for a bit, the more expandable bit cools and the part closes, again turning the item On. This is the principal used in blinking Christmas tree lights and, in a more complex manner, thermostats (for those who wanted to know).

* A bimetallic strip is a piece of metal made by laminating two different types of metal together. For more information check How Stuff Works. [Interesting site, but annoyingly full of ads sending cookies.]