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Field Notes

Covering the natural wonders of the Pacific Northwest

June 3, 2011 at 11:00 AM

Beating sunburn — when you can’t move into the shade

Notice that luminous, shiny coating on many new leaves as spring finally spurs new growth this year? Beautiful as it is, it has a definite purpose. Especially on days like today.

It’s a wax layer the plant manufactures to protect tender new growth from UV radiation, notes Soo Hyung Kim, Assistant Professor at the University of Washington.

The waxy coating sprayed on apples and other fruits by packing sheds is a knock-off of this natural defense that plants mount as they unfurl new leaves. Not only does it protect against sunburn, the coating also keeps in moisture — a plus if you are a trying to keep apples crisp.

The coating degrades as leaves mature — something to think about when you are tempted to skip the sunscreen. The same radiation that damages the wax hurts your skin, too.

The softness of new leaves is part of their growth process, Kim explains. When they are young, the walls of cells are soft and supple, to allow them to continue to grow. The cells become rigid once they have reached full size.

You can observe both the waxy coating and the softness of new leaves vividly in Oregon grape. Sharp enough to prick your finger with the tiny thorns at the tips of last year’s leaves, and colored a dull, dark green, the new leaves on this native shrub are entirely different. Soft, with no sharp points at all, and shiny as if polished: that’s the new growth for this year.

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Oregon grape stretches out its soft, shiny new growth. Photo by Lynda Mapes

The plant’s growth this spring actually was initiated last year, when buds formed containing the cells that are growing now. The first leaves unfurled create the carbohydrates the plant uses to keep growing.

Some plants also sport hairs on their leaves and stems to prevent moisture loss. Feel the stems of common foxglove, Digitalis purpurea. They are soft as a baby’s ear, and furred all over with miniscule white hairs that give the plant a glow when back lit.

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Furred with tiny white hairs, the stem of foxglove is velvety to the touch. Lynda Mapes photo

The hairs create a humidity layer along the surface of the plant, notes Sarah Reichard, director of the UW Botanic Gardens. “That’s why they go to the trouble to grow all that hair.”

The heart drug digitalis is derived from this plant, which is highly poisonous. It’s name digitalis is from the Latin word for thimble — a reference to the shape of the blossoms that adorn the tall, waving wands of these beautiful plants, introduced to the Northwest Coast from Europe.

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