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Horticulture 1000
HT1091 - Plant propagation 1 - Seed development
Session 2 - Seed development
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Seed development

The process by which seeds are formed is almost unbelievable. The flowers in this picture are grown to make a garden look attractive. However, their main purpose is to contain the sex organs for the plant.

This is a fuchsia plant in flower

This is a fuchsia plant in flower.

Here is a diagram of a fuchsia flower.

Let’s look more closely at flowers, as this is where all the action happens for sexual reproduction in plants.

Here is a cross-section diagram of a fuchsia flower.

Complete Activity 2A in your workbook.

Pollination

Cross pollination of a flower Cross pollination of a flower.
Self-pollination of a flower Self-pollination of a flower.

Pollen travel

There are two main ways that pollen gets from one flower to another:

Insect pollinated

Insect pollinated

When insects like bees or flies visit flowers and pollen sticks onto their hairy legs. When they visit another flower the pollen rubs off on its stigma.

Insect pollinated flowers may have large brightly coloured petals, large pollen grains, and be scented.

Wind pollinated

Wind pollinated

The wind carries pollen from one plant to another. Wind pollinated flowers may have small petals, no scent, a lot of small light pollen grains on long, droopy stamens.

Grass pollen is carried by wind. Grass has feathery stigmas to catch the pollen.

Complete Activity 2B in your workbook.

A few plants, for example, cucumbers, have separate male and female flowers on one plant.

Female and male cucumber flowers Female and male cucumber flowers.

Kiwifruit have male and female flowers on separate plants. These are called dioecious plants. This means a male plant must be grown alongside female plants for pollination to occur.

Fertilisation

Once pollination has taken place fertilisation can occur. Fertilisation is the joining of a male and female sex cell. This is what happens:

The process of fertilisation

The seeds will have characteristics from the two different parent plants. Just like you, they will be individuals and in some way different from their parents.

The development of seeds

Seeds contain a food store and a tiny plant inside a protective coat.

The food store is called the cotyledon.

Monocotyledon seeds, such as corn, have one cotyledon to store food for the developing seed. Some seeds such as bean seeds have two cotyledons. These are called dicotyledons.

The tiny plant is called the embryo, and the protective coat covering the seed is called the testa.

Understanding the structure of seeds will help you propagate plants more successfully from seed.

This is a diagram of the inside of a split lupin seed.

Lupin Seed

Complete Activity 2C in your workbook.

Cross-section diagram of a corn seed

Here is a cross-section diagram of a corn seed.

It has one cotyledon. It is called a monocotyledon seed. The cotyledon’s role in a monocotyledon is slightly different from that of a dicotyledon. The cotyledon transfers food to the embryo.

Fruit formation

When fertilisation is complete, the ovary surrounding the seeds develops into a fruit. The fruit helps to protect the seed. Some fruit is dry like gorse or lupin pods and some are juicy like an apple.

Seed dispersal

This is the scattering of seeds away from the parent plant. Seeds need to be dispersed to reduce the competition from the parent plant and germinating seedlings.

When the pod of the lupin dries it splits open explosively to scatter the seeds away from the plant.

A lupin seed pod dispersing seeds

Seeds can be dispersed by the wind, on animal hair or bird feathers, in bird and animal faeces or they can float in water.

Complete Activity 2D in your workbook.

Key points   Key points

  • The process of pollination and fertilisation in plants explains why plants grown by seed show some variation.
  • Pollination takes place when the pollen grains are transferred from the male anther to the female stigma.
  • Fertilisation is the joining of the female ovule and male pollen.
  • The new plants will be slightly different because all ovules and pollen grains are slightly different genetically.
  • A monocotyledon is a plant with one cotyledon in its seed.
  • A dicotyledon is a plant with two cotyledons in its seed.

What's next?

Go to: 3 Seed germination.

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