Anther

In botany, it is as important to study the parts and functions of the flower as it is that of plants. The anther is a part of a flower. Let’s start by learning the parts of a flower, pistil, stamen, receptacle, peduncle and sepal. To define anther, it is crucial to understand the reproductive parts of the flower. The female reproductive part of a flower is the pistil, composed of stigma, style and ovary. And the male reproductive part of the flower is called the stamen. The anther is attached to the part of a flower’s male reproductive system called the stamen. The male structure stamen is composed of a filament that is a long tube with an oval-shaped pollen-producing structure attached to the top of it called the anther. The anther is solely responsible for producing and bearing pollen that serves the purpose of fertilization in flowering plants. Only upon pollen production by the anther does the pollination commence.  

 What are the Various Types of Anther in Flowering Plants?

Anthers are bilobed structures attached to the slender filament (that carry the pollen sac) of a stamen in a male flower. Anthers show various morphological variations in different species of flowering plants.  Anthers may be classified based on its lobe structure and type of attachment to the filament. Based on the structure and shape of the anther lobe, it is categorized as bilobed, unilocular, linear, rounded, sagittate, appendiculate, reniform, etc.

Male Reproductive Part of the Flower

The male part of the reproductive system of the flower is called Androecium that is individually segregated as the stamen. The stamens are elongated filaments raised in the middle of the flower in a circular ring. There are at least five to six stamens in a flower. The ratio of the number of stamens is the same as that of the petals but sometimes it varies depending on varieties of flowers and their species. Anther of a flower and filament are the two parts of the stamen that surround the pistil. Anther meaning and role can be particularly understood better when you look at the diagram below that suggests the location of the anther. It also depicts the other parts very clearly for a clearer understanding and one can refer to when reading about anther. 

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Parts of a Flower

As understood from the above diagram, stamens are separated but all connected and collectively the stamens are called androecium. A filament of the stamen very diligently holds the anther on top and facilitates its functions. The filament holding the anther is attached to the petal, and the nature of the stamen solely depends on the type of the plants and flowers. The plants that reproduce through self-pollination which is via the transfer of the pollen from the anther to the stigma of the pistil to reach the ovary of the same flower of the same plant has the stamen bent towards the pistil. In the case of plant reproduction via cross-pollination, that is the stigma receives the pollen from flowers of other plants via various means like insects and wind; the stamen is usually bent away from the pistil. 

Anther and Stigma 

Anther of a flower is often confused with stigma even though their functions in the flower serve different purposes. Let’s take a look at what the anther contains versus the stigma. Anther and stigma are the male and female reproductive parts of a flower respectively. 

Anther versus Stigma

Structure and Function of the Anther

The function of the anther is to produce and provide the pollen, the pollen containing anther acts as the sperm that is necessary for reproduction. The anther functions in attracting pollinators, such as bumblebees and other insects to the flower who via sucking on the nectar does aid in both self-pollination and cross-pollination. And reproduction would be impossible without this crucial part of the flower's anatomy that is the anther. 

For the understanding of pollen production, it is important to understand the structure of the pollen-producing oval structured anther.  

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Transverse Section of the Anther of a Flower

The anther which is the fertile part of the stamen usually has two lobes or thecas connected by a connective. Each lobe contains two pollen chambers longitudinally placed. Each chamber filled with pollen or pollen grains is also called microspores and hence these chambers are also called microsporangium. 

Four layers in total surround the pollen sac or pollen chambers, and they are namely, Epidermis, the inner epidermis or endothecium, the middle layer and the tapetum. 

1. Epidermis - it is the outermost layer and is a single layer that is of thickened fibrous matter whose function is to protect the pollen sacs.

2. Endothecium or the inner epidermis is a single layer of radially elongated cells that develops cellulose with pectin and lignin fibrous thickening around the sac which holds it together and prevents it from splitting or bursting open.

3. The middle layer is a thin-walled cell of three to four layers situated just below the endothecium nourishes the microspore for facilitating pollen production. 

4. The fourth layer that lies closest to the pollen sac is nutritive and provides necessary nutrition for pollen division and pollen generation.

The anther with two thecas are called dithecous anther and these are very common. Dithecous means two thecas or lobes; it can also be referred to as bilobed. Some examples of bilobed or dithecous anther containing flowers are Solanum and Crotalaria. Some flowers of the plants, however, only have one lobe or theca that produces pollen. Such ones are called monothecous anther. Examples of a monothecous anther are Hibiscus.

How do plants Reproduce?

Plants are essentially sexually reproducing organisms. As discussed above, angiospermic plants have stamen and carpel as the male and female reproductive parts, respectively. The flower may have both the male and female reproductive parts in the same flower (monoecious) or in different flowers (dioecious). The flower with only the male reproductive parts is said to be androecious. While the flower with only female reproductive organs is called gynoecious. Sometimes, a flower may have both the reproductive parts but one of them, either the stamen or the carpel, have lost their functionality (an adaptive feature to prevent self-pollination). Such flowers may be known as staminate (non-functional carpels) or pistillate (non-functional stamens).  Sexual reproduction occurs by means of pollination. Pollination is the process by which the male gametes of a flower (pollen sac) is transferred to the stigma of the female reproductive part of a compatible flower. Pollination occurs by various natural and environmental agents. Wind, water, animals, birds, etc,  all act as pollinating agents to different plant species.

Once the pollen grain from the pollen sac is received by the stigma, it germinates to form a long slender pollen tube that carries the two male gametes to the ovary, where it fuses with the female gamete to form the zygote and the endosperm nuclei. It is also represented as 2n + 3n. The flower then matures to lose its carpel, petals and other non-essential flowering parts, while the ovary enlarges and develops into the fruit. The ovule becomes the seed, which contains the embryo and the endosperm for the developing embryo.

Fun Facts about Anther

1. Since the anther’s main function is to aid reproduction via pollination, the base of the stamen consists of nectaries that attract the pollinators like insects, mainly bees like bumblebees to carry out this function.

2. The nectaries provide food to these pollinators as a reward from nature to carry out pollination.

3. The pollination process via the anther is also carried out by water, wind, animals and birds.

4. The microspore containing pollen sac that produces pollen is called microsporangium or pollen mother cells.