THE FLOWER......

 

 

 

 

 

 

 

 

 

 

Welcome..... The flower is the beginning of our adventure, and it will be the end of it.

What is a flower, anyway?

We have all seen flowers in one place or other.

A flower is a sexual organ in flowering plants. Flowers may arise from the axial or grow clusters forming an inflorescence as in the sunflower.

The general parts of a flower show four main whorls that include Petals (corolla), Stomata (Androecium), Sepals (calyx) and Pistil (gynoecium). These shall each be dealt with further on.

An incomplete flower is one in which one or more of the four floral whorls are absent.
The non-essential organs of a flower are the calyx and corolla. The essential are pistil and stamen. A flower in a diameter through it divides it into two similar halves is called a regular flower. One, which does not produce two similar halves, is called irregular flower

A hermaphrodite is a flower with both female and male organs. Flowers with either stamens or carpels are called unisexual. For stamens are called staminate while for carpels are called pistillate. However a plant may produce both pistillate and staminate separately born on the same plant is called diocious.

-The petals are those colorful plaps of material that we usually call the flower.

Collectively, petals make up what is called the corolla.

These are usually united to a corolla tube and protect the stamen (filament and anthers) and carpel (ovary, stigma and style). (to be studied further on)


Arrangement and number;
In Dicotyledonous plants the petals are usually present in fours, or fives or multiples of fours and fives. In monocotyledonous the petals are present in three or multiples of three.The arrangements vary with species and are unique to a given species.


Scent and color;
Flowers with brightly colored corollas are usually large.They are also usually insect pollinated. Sometimes the color may be green or another dull color, and sepal-like.Such petals are referred to as sepoloids.


Arrangement;
Petals that are joined in a cup are called gamopetalous and those that a free are called polypetalous. They may exhibit one of the following arrangements; a valvate, imbricate or contorted arrangement.

-Sepals are those usually green colored culs beneath the petals. Collectively they make up what is known as the calyx.There are usually two to five sepals on a plant.


Color and shape;
Sepals are usually small and green sharp pointed at the tip.

Sepals serve to protect the flower in the bud stage. Sepals of some flowers may be large, brightly colored and attractive; such sepals are called petaloids.

Arrangement;
Sepals may be close together or free from each other for example crotalaria. Where the sepals are joined they are called gamosepalous and where they are free they are called polysepalous.

Where sepals and petals look alike or are joined together they are referred to as perianth with each unit of the perianth being called an epicalyx.

A polypetalous calyx will exhibit three main arrangements…..

 

Within the protective cover of the petals and sepals is an intricate arrangement of organs of immense importance.......

A nectary: this is a group of glandular cells situated at the base of the corolla or pistil or within the receptacle. It secretes some sugary solution called nectar. This acts as food for many insects such as honeybees and butterflies. It plays and important part in pollination.

The Stamens is made up of the anther head and the filament. It is the male part of the flower. Another name for the stamens is the androecium.

In dicots there are fours and fives or multiples of fours and fives. In monocots they are in threes or multiples of threes.


Arrangement; Filaments may be free or joined. The filament may be joined into a tube as in most legumes.
Appearance: A long shaped anther is usually a characteristic but usually varies with species. The anther is usually bi-loged with each anther containing two pollen sacks hence each anther will pass four pollen sucks after the walls separating two pollen sucks breaks down giving rise to one pollen suck in each room. Sometimes the two anthers may be connected by a strip of tissues called connectire

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Pollen Grains
Inside the pollen sack lie the pollen grains, which contain the male reproductive gametes. They consist of fine dust-like particles often yellow in color but of different shapes and sizes in different plants. The commonest shapes include round triangular and Ovoid. Each pollen grain has two contraire coats, the outer coat which is a tough cutinised layer is called exine and encloses a more delicate cellulose layer called the intine.

The pollen grain has two nuclei, whose respective functions will be mentioned under fertilisation.

The female part of the plant is called the pistil or the gynaecium. It consists of the ovary and its contents, the style and the stigma.

The ovary is made up of a number of carpels, which enclose a number of ovules the ovary may be formed from a single carpel, which is called macrocarpellary. The ovary may also be formed from many carpels, which is referred to as polycarpellary. In situations where the ovary is made up of many carpels they may either be free or joined if free they form apocarpous ovary. If joined they form a synccarpous ovary. The role of the placenta is to attach ovule to ovary.

The placenta is made up to ridges of soft fleshy tissue.
A funicle is a short stalk suspending an ovule from the placenta.
Placentation is the arrangement of ovules and placenta within the ovary. This varies from flower to flower. The major types of placentation are marginal, parietal, axile free central, based and Superficid;( discussed else where).
Other parts of the pistil are style and stigma the style may be long or short usually forming a tube carrying a stigma may be single or multiple free or joined.

The ovary contains the feamle gametes, called ovules. They are the cells that join with the pollen cells to form the seed.Each ovule consist of a large oval shaped cell called the embryo sac. The mature embryo sac contains a number of nuclei including the female nucleus or ova.

Since the ovules are within the ovary, it follows that the ovary in most plants becomes the fruit after fertilisation while the ovules become the seeds.in some however, other parts develop into the bulk of the fruit. These are discussed under fruits.

The general structure of the ovary varies from species to species.

An inferior ovary is an ovary where by the ovary is completely embedded in the fleshy receptacle and the corolla such that the other floral parts arise from a point higher than whole flower is called Epigynous.

A superior ovary
When the floral parts arise at same level as the ovary or below It. In this case the whole flower is called Hypogynous.

An inferior ovary(II)
The ovary lies in the center of the flower but because the receptacle is cap-shaped the other floral parts appear to be attached slightly above the ovary.
The whole flower is called Perigynous.

The study of the flower is continued by viewing the process of pollination, and after that, fertilisation.

For more information you could search the web, or visit our related links page.....