Welcome to this first lesson from
Botany for Young People by Professor Asa Gray. In this lesson, we will learn all the main parts of a plant, including their vegetative parts, reproductive parts, and all the parts of a flower. Are you ready? Let's go!
Plants are made up of three main parts - roots, stems and leaves. These three parts are all a plant needs in order to grow and survive.They are called the vegetative organs of a plant.
Plants also produce flowers, fruits and seeds; but, they do not need these to grow and survive. These are the reproductive organs of a plant. They create new plants to help the species survive.
Vegetative Parts of a Plant
Let us look at the vegetative organs, or parts, of a plant. As we read above, these are made up of three things - the roots, stems and leaves.
Roots have two main purposes in life: to stabilise the plant in the earth; and to absorb water and nutrients from the soil. Roots grow downwards into the earth and branch into smaller roots, called rootlets.
The stem, is the part of the plant that grows up towards the sky. Like the roots, it has two main purposes: to support the leaves, flowers and fruits; and to carry water and nutrients between the roots and the leaves.
Leaves are usually thin, flat and green. They grow with one face towards the earth and one face towards the skies. They absorb nutrients from the air and use sunshine to turn these nutrients, plus the nutrients absorbed by the roots, into food the plant can use (we will learn more about this in another lesson.)
Reproductive Parts of a Plant
Now it is time to learn more about the reproductive organs of a plant. Like the vegetative organs, there are three of these - the flowers, fruits and seeds. Let us learn about each one in turn, starting with the flower.
Look at the pictures of these flowers. Each one is made up of two parts - a green bit, and a colourful bit. Can you see them?
The green leaves at the bottom of a flower, are called the calyx. The colourful bit of the flower, is called the corolla. Let me take a flower from the morning glory, and separate the two out so you can see them.
The calyx is known as the outer cup, or outer leaves of the flower. This is the part that protects the flower while it is still in bud. Each of its leaves in called a sepal.
The corolla is known as the inner cup, or inner leaves of the flower. The colours of the corolla help attract insects like bees and butterflies to the flower. They also protect the important structures in the middle of the flower. Each of the corolla's leaves is called a petal.
While many flowers have both a calyx and a corolla, some do not. The tulip only has a corolla - it is missing its calyx. Spurge flowers have neither a calyx nor a corolla; and the 'flowers' of the clematis plant, are actually a special, colourful calyx - it does not have a corolla!
The Parts of a Flower
Now it is time to take a closer look at the structures inside the flower. I am going to take the corolla of our morning glory flower, and carefully cut it down the middle to open it up for you. Have a good look and see what you can spot inside. Can you see five long, skinny things? These are called stamens.
Let us very carefully take one of the stamens out so we can have a look at it under a magnifying glass.
You can see it is made up of two parts - a large knobbly bit at the top, and a long, skinny stem underneath. The large knobbly bit is called the anther. It has a slit down each side, so the pollen can come out. The long, skinny bit, is called the filament. This holds up and supports the anther.
Here is another morning glory flower. Look closely in the middle of the flower. Apart from the five stamens, can you see another structure? Look right in the middle. There is another long, skinny stem with a pale, knobbly bit on top. This is called a pistil.
Unlike the stamens, the pistil is made up of three parts - an ovary, style, and stigma. Let's carefully take the pistil out of this flower so we can examine it more closely under the magnifying glass.
Do you see the larger, knobbly bit at the bottom - the part that is sat on top of the green stem? This is called the ovary. If the flower is pollinated, it is this bit that becomes the fruit.
The smaller, knobbly bit at the top, is called the stigma. The stigma is very sticky. This is to help catch any pollen that lands in the flower, so it can be pollinated (we will learn about this in another lesson.)
The long, skinny stem in the middle, is called the style. This holds up the stigma to help it catch pollen, and connects it to the ovary.
Now let us look at the stamen and pistil of another flower - a lily. What differences can you see between them?
Hopefully, you can see that the colour is different. The anther of the lily is orange-brown, whilst that of the morning glory is a very pale yellow. The colour of the filament and style is different too. But can you notice any difference in the size of the ovary? The ovary in the lily is much, much bigger. This makes it easier for us to handle and examine.
Let's carefully cut one open and have a look inside. I am going to take two lily pistils and cut one ovary down from top to bottom, and the other across the middle, so you can have a good look.
Do you see those white things inside the ovary, that look a bit like teeth? Those are called ovules. If the flower is pollinated, these ovules become seeds.
Once a plant has finished flowering, its calyx, corolla and stamens may fall off. But the pistil will almost always remain. If the flower has been pollinated, the ovary will grow bigger and bigger, becoming the fruit - and the ovules become the seeds inside the fruit. (When we say fruit, this can mean a berry, a stone fruit, a grain, a pod or a nut.)
Look at these pictures. They show a young morning glory pod with the remains of its style still on top; and the pod once it has fully ripened and matured.
Can you see how the mature seed pod has split into three sections? These are called cells, or cavities. As the pod dries out, these split open to release the seeds. Both the morning glory and the lily have three cells each. But, there are only two seeds in each of the morning glory's cells, while a lily has many seeds in each of its cells.
Let's have a look at a morning glory seed. I have taken two other seeds and cut them down in different directions so we can have a good look inside. Can you guess what the light coloured thing inside the seed might be?
Let us soak another seed and carefully take this pale thing out. Do you have any ideas what it could be now?
It looks a bit like a little leaf now, doesn't it - and indeed, so it is. In fact, it is two leaves, stuck closely together, one behind the other. These are the very first, pulp, baby leaves of a little baby plantlet. Look back up at the pictures of the seed. Can you see how it was all crumpled up to fit inside?
Now, let us carefully separate out the two leaves and see it for what it is - two little leaves and a little stem. These little leaves are called seed leaves, or cotyledons. The little stem, or stemlet, is called a radicle.
Examine the pictures of the seed again. Can you see the cotyledon and radicle inside them?
Alright! We have reached the end of this first lesson. I hope you have enjoyed it? Now it is time for you to put your knowledge into practice.
I would like you to take a nature walk and look for some plants. Can you identify the vegetative and reproductive organs of three different plants? Next, find five different flowers. Examine them carefully to identify their calyx, corolla, stamens and pistils. Can you spot all four things, or are they lacking any?
Draw or write your thoughts and findings inside your journal or nature notebook.
See you for the next lesson!
