Saturday, June 20, 2009

An Orgy in the Garden!

The goings-on in the Community Garden are definitely x-rated, but the nice ladies who diligently water, weed and tend to their little plots are missing the entire thing!

Well girls, what do you think all that flowering and fruiting is about? And where do little seeds come from? Time to take these innocent gardeners behind the woodshed and share the facts of life with them. Hold on to your sunbonnets!

Flowers are the sexual organs of flowering plants. (blush) I don't know how anyone else feels but I worked hospital wards for years and for looks I think almost any flower beats the heck out of what we've got to work with!

There are two types of reproduction in plants: ASEXUAL and SEXUAL

Asexual reproduction (as practiced by mushrooms or plants which send out runners or suckers) requires only one parent. No mate is needed, all offspring are genetically identical to the parent and there is no diversity in the species. This is potentially dangerous because the entire species can be wiped out by a pathogenic, environmental or climatic disaster. If one is vulnerable, all are vulnerable since none of them will have any greater resistance than its clone.

But flowering plants use sexual reproduction and they have developed it into an art form. Flowers can be pistillate (female), staminate (male) or perfect (both male and female).

Sexual reproduction requires two parents, a male and a female, both of which contribute DNA. (Any mother will understand this perfectly well since all of a child's irritating traits come from their father's side of the family.) Sexual reproduction insures genetic diversity, which is needed for vigor. Each new offspring is genetically unique.

So peeping through the petals we see the Androecium - the male reproductive part of the flower. The individual units of androecium are called the stamens. Each stamen has a thread-like filament at its free end where a four-lobed anther is attached. The anther contains four pollen-sacs, one in each lobe. These pollen-sacs produce pollen which contains sperm cells. When the pollen is mature the anthers burst open and the pollen is released onto the surface.

The Gynoecium is the female part of the flower. The individual units are called the carpels or pistils. A flower may have any number of carpels each of which is made up of an ovary, a hollow tube called a style (think fallopian tube), and a stigma. The ovary contains many ovules each of which consists of an egg and associated cells. The stigma is a sticky structure that receives the pollen. The style is hollow and provides a passageway for the sperm to reach the eggs.

Transfer of pollen to the stigma is called pollination. When the pollen is transferred to the stigma of the same flower, it's called self-pollination. If the pollen grains are transferred to the stigma of another flower of the same species it's called cross-pollination. Cross pollination is helped along by wind, water, bees, birds, bats and other animals including people who stick their noses into one flower after another. That's the reason for the extravagant colours, the lush fragrances, the nectar, the wild shapes. It's all a part of the plants' strategy to attract some creature which will carry out its reproductive cycle.

When the strategy works and a grain of pollen reaches a stigma, the pollen grain immediately puts out a tube which grows down the style and enters the ovule where it bursts at the tip releasing a two-man sperm team. One sperm fuses with the egg and fertilizes it. This results in the formation of single cell with both parent's DNA - the zygote - which develops into the seedling. The other sperm fuses with a separate part of the egg and forms the endosperm, the plant equivalent of the placenta, which nourishes the zygote. The ovule then becomes the seed and the ovary changes into fruit. Think tomato - the ovule becomes seeds and the ovary gets sliced and eaten with your salad.

And the reason I was out in the garden with a paint brush this morning - no matter how small the blossom, a female squash blossom always has a micro-version of the squash it will eventually produce behind it. If there's no baby squash behind the blossom it's a male blossom. And unless that male blossom has a chance to get its pollen over onto the female blossom's pistils, her baby squash will wither and fall off. No sentimentality. Fertilized ovules get all the energy, because they carry the genetic material of that plant forward to next year. I was out making whoopee with the squash.

And that, ladies, is as why I am able to say there's an orgy going on in our gardens.

No comments:

Post a Comment