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[Screaming Eagle]

Sex in the Backyard
Or
Basics of plant flowering and reproduction

This is the seventh in a series of articles on basic botany with a slant toward bonsai growers. Our goal is to better understand some of the basic principles regarding plant structure and function in order to help us grow healthier bonsai. Most of the information in this article in particular is taken from a basic college biology text ' The Nature of Life' written by John Postlethwait and Janet Hopson. The book was published by McGraw-Hill in 1995.
This article will cover some very basic information about flowers and their structure as well as their role in plant reproduction. We will also discuss seed germination as well as tissue culture and some possibilities for bonsai growers.
We usually don't think of flowers as sex organs, but that's exactly what they are. Flowers are simply showy sex organs for plants that help to get the job of reproduction done in a most graceful and efficient way. They are modified shoots that contain the reproductive organs of all plants including grasses, trees as well as some of the more familiar roses and azaleas. Flowers produce pollen grains that contain sperm nuclei and sacs that contain egg nuclei. The various parts of the flower insure that the transfer of pollen to the egg sac will be successful.
There are 4 layers of structures of plant flowers; from the outside in, they are sepals, petals, stamens, and carpels. The inner 2 rings function in actual reproduction and form gametes while the outer 2 rings basically just look good. What sometimes looks like flowers aren't actually true flowers at all. Bougainvillea for example are beautiful flowering tropical vines with showy….bracts. The flowers are actually tiny white formations inside the flashy bracts. Bracts simply surround the flowers for show. Ordinarily, the sepals and petals in the outer rings have showy colors, shapes, and fragrances that attract animal pollinators.
The structures in the inner 2 rings (stamens and carpels) do the actual sexual work of producing eggs and sperm for the flower. The stamen is the male reproductive structure that is pin-shaped and produces pollen. Some flowers can have more than 1 (sometimes several) stamen. Within each stamen is an anther (contains pollen sacs) sitting on a filament (shaft of the pin). The long filaments help with wind-pollinated plants. Carpels form the innermost ring of flowers and are the female parts of flowers. They are usually shaped like a wine bottle and the ovary is at the base of the carpel. Eggs are contained in the ovaries and it is these eggs that eventually form into seeds. The stigma is supported by the neck of the ovary and is a sticky surface that traps pollen for germination. Crossing varieties of plants is as simple as mixing the stamen to the stigma of each variety and waiting for the seeds to develop.
Some flowers have both male and female parts and are referred to as perfect flowers. Other trees have either male or female parts and are called imperfect flowers. Some species of trees have male flowers separate from female flowers on the same plant. Others have only male flowers or only female flowers on individual plants. It seems that characteristics of flowers play an important role in how the flowers are pollinated also. Rather than attracting members of the opposite sex like peacocks, they attract pollinators for that particular type of plant. Bees see some colors well while birds and moths see other colors better. Flowers that are generally pollinated by wind are not brightly colored or highly fragrant.
Germination of seeds takes place usually in spring. Small seedlings use nutrients and water at a higher rate and eventually crack out of the seed coat. Some seeds need to be scarified or artificially cracked in order to germinate. Acacia seeds and Baobab seeds in particular must be submitted to some rather grueling processes by man to encourage germination of seeds or they will simply lie dormant for years. Once the tiny radicle of the new seedling slips out of the seed coating, the young root pushes downward into the soil, the shoot pushes upward through the ground and lifts the cotyledons toward the sun. Cells begin to divide in the apical meristems of the shoots and roots, the first normal leaves develop, and photosynthesis begins. From that time on, the plant is truly independent.
Once a given leaf begins to develop, a bud primordium forms in the upper angle between the young leaf and the stem. This immature structure continues to develop into a bud which can develop into either flowers or branches depending on the type of plant it is. The floral buds develop into flowers, the blooms are pollinated, the eggs are fertilized, embryos develop, and new generations of seeds are developed.
One more very interesting characteristic of plants is their ability to reproduce from small pieces of tissue. Essentially, developers punch out a piece of plant tissue from a leaf or stem, place it into a nutritious medium with warmth and light and wait. The cells lose their recognition of identity as leaf or stem and begin to form a callus that is basically undifferentiated tissue and sometimes single cells. It's placed into a culture medium with growth hormones to promote differentiation and from there they develop into small plants. Each plant cell contains the complete genetic information for a whole plant and the plants can be raised as true representations of the parent plant. This process avoids the wild swings in plant variation as a result of being raised from seeds because they have the identical genetic information of the parent plant.
So much for our exploration of flowers and plant reproduction. Maybe the next time you walk into your backyard or garden you'll be moved to examine some flowers closer to get a better idea of what's actually happening. Next we will explore growth regulation factors in plants including the various plant hormones and their effects on plant growth. If you haven't renewed your subscription to our newsletter, be sure to do so before then because this information will prove to be very useful in our everyday pruning and growing of bonsai. Have fun.