3/11/04

Contacts:
Linda Naeve, Reiman Gardens, (515) 294-8946, lnaeve@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Reiman's Pick for the week of March 8, 2004

Seeds are Nature's Miracle

By Linda Naeve
ISU Extension Coordinator,
Reiman Gardens

This week's Reiman's Pick focuses on an important part of the life cycle of many plants, the seed. Seeds are vital to the survival of plant species, but once the plant is growing and blooming, this stage of a healthy garden is easily forgotten. This is understandable because seeds appear to be dead or almost inanimate, especially if they have a hard, glossy coat resembling small pebbles on a beach.

On closer inspection, seeds are fascinating living organisms that are as diverse as the plants they become. Seeds range in size from tiny petunia seeds that resemble specks of dust to the large, softball-sized coconut seed. The variety of seed is quite diverse from glossy to dull, solid-colored or speckled, round, flat or oblong.

Although lacking a brain, seeds almost seem to have their own form of intelligence. Seeds use several dormancy mechanisms to prevent them from germinating at the wrong time. One of the most interesting examples is the acorn. An acorn will not germinate and start to grow until after a squirrel buries it. A chemical in the seed, called abscisic acid, induces dormancy in the embryo. This prevents it from growing before it has been exposed to a cold period, such as winter. Gardeners artificially induce these seeds to germinate by storing them in a moist, cold environment for several weeks. This treatment, called stratification, induces certain enzymes in seeds to degrade the abscisic acid. This process enables the seed to sprout after it is planted in warm, moist soil.

Seeds of desert plants have a different challenge that involves moisture availability rather than temperature. Desert plants contain compounds that keep them dormant until the proper season for germination. When the wet season arrives, rain soaks the seed, breaking down the water-soluble compounds. This helps the seeds absorb water and germinate.

The thickness of the seed coat also affects germination. For example, morning glories, sweet peas, and many other plants with thick seed coats stall germination by keeping water away from the seed. Eventually, water seeps to the seed when the coat is damaged or worn. Gardeners weaken a thick seed coat by scarification which is simply filing, nicking or soaking it in water.

Nature handles the scarification process for some plants including strawberries and raspberries. First, an animal must eat and swallow these fruits passing the seed through its digestive system. This process weakens the seed coat but does not harm the embryo inside. Once on the ground and given a little moisture, the seed will sprout.

Light is another mechanism plants use to insure proper germination. For example, small lettuce seeds require light and will not germinate if buried too deep.
Another fascinating fact about seeds of any size is they contain all the food needed to sustain the growing embryo until it reaches light and can start manufacturing its own food.

Recently, seeds have been the focus of attention at Reiman Gardens. According to Ed Moran, assistant garden superintendent, volunteers and staff have transplanted 22,620 seedlings of 400 different varieties that will beautify the Gardens this summer.

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Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The picture's fullsize photo is 172K. Caption: seeds

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