Plant sex

By: Nancy Olsen

I knew I could get your attention with a discussion on the fundamentals of plant reproduction. In the months of January and February, many seeds are sown in the hopes of germination taking place and growing into a plant that will soon be placed in a flower bed. Propagating plants by seed requires a gardener to understand the basics of sexual reproduction in plants.

For every seed produced, a single pollen grain and a single egg are required. For example, every seed in a tomato is produced from the genetic contents of a single pollen grain and the ovule which contains the egg cells.

Sometimes a fruit is confused with seeds. Fruit is the way nature packages its seeds. Seed that is properly packaged has the greatest opportunity to be relocated to a suitable growing area. A seed consists of three parts: the embryo, food storage tissues, and seed coverings.

The fruit is a ripened ovary which consists entirely of the tissue of the mother plant.

When you eat an apple or pear, you are eating fruit tissue (or a ripened ovary). The portion you normally throw in the compost (core) contains the ovules which contain the seed.

Seed and embryo development control much of the growth of the fruit. Thus, good pollination is required to produce good sized and nicely shaped fruit in many plants. Some plants can produce viable seed from self pollination while other species require pollen from genetically different individuals. This is why many varieties of apples, pecans, peaches, blueberries, chestnuts, and many other fruit crops require a specific pollinator. Other plant species are successful in pollinating themselves (like tomatoes or beans) and do not need special pollinator varieties. In special cases, plants have been selected by man to produce fruit without seed (banana, seedless watermelon, Thompson seedless grape, ect…).

Plant seed comes in many sizes. For instance, the seeds of particular orchid family members are known to produce very small seed (millions of seed per pound), while the coconut (the husk around the coconut is the fruit) represents a very large seed.

Seed germination represents the earliest stages of plant growth. The embryo in the seed must be alive in order for germination to occur, and appropriate environmental conditions must exist. Seeds from the apple, pear, rose, peach, cherry, pecan, camellia, and maple have a dormancy requirement for germination. They each require a particular number of days/weeks/months of moist-chilling (40F temperature or less) as a minimum requirement for optimum seed germination. This moist-chilling treatment is called stratification. Seeds can be stratified by mixing the seed with moist sand and sealing the sand-seed mix in a plastic bag, and placing in the refrigerator. Seeds can also be directly planted in the soil during autumn but seedling loss can be high due to critters and competition.

The embryo of some species are so well protected by the seed or fruit covering that the covering actually prevents the young embryo from growing. The seed may need scarification. This process may be done by cutting the seed coat with a file, cracking it with a hammer, rubbing the seed with sand paper, or soaking the seed in acid. Clover, canna, cotoneaster, witch hazel, and thousands of other plants require scarification before the seed can germinate. The digestive tract of birds or animals often make the best natural plant seed scarifier, for obvious reasons.

Many species of plants require both stratification and scarification before the seed will germinate. Each species of plant has its own special requirements for seed germination.

A cheaper method would be to contact a local NC Cooperative Extension Agent. Nancy Olsen, who can help with yard concerns, can reached by calling 910-862-4591 or visiting the office at 450 Smith Circle Dr., Elizabethtown.

Nancy Olsen