What does a seed need to germinate?

What is germination?

When a seed turns into a sprout, it is said to have germinated. The outer covering of a seed is the seed coat. Inside it is a tiny embryo, which can develop into a whole plant if it gets the right conditions. But which conditions? An experiment with four pots finds out.

The four-pot experiment

Fill four identical pots with garden soil and sow four bean seeds in each. Keep them like this for about two weeks and look at them every day:

• Pot A: in direct sunlight, with no water at all.
• Pot B: in direct sunlight, with so much water that it always stands above the soil.
• Pot C: soil kept slightly moist, in a dark place.
• Pot D: soil kept slightly moist, in direct sunlight.

Pot	Air, water, light	Germinates?
A: sunlight, no water	Air and light, but no water	No
B: sunlight, excess water	Water and light, but no air	No
C: moist soil, dark	Air and water, but no light	Yes
D: moist soil, sunlight	Air, water and light	Yes

The seeds germinate only in pots C and D, which both have the right amount of water and air. Pot C shows that light is not needed for germination.

Why water and air?

• Water: seeds need water to carry out the processes needed for growth. Water softens the seed coat and helps the embryo inside develop into a plant.
• Air and soil: seeds use the air in the spaces between soil particles. These spaces also let roots grow easily. In pot B, standing water fills the spaces, so the seeds get no air.
• Light or dark: most seeds, like beans, do not need light to germinate. After germination, though, the seedling needs sunlight to grow further.

Some seeds are different. Seeds of Coleus and Petunia need light to germinate, so covering them with soil stops them from sprouting. Seeds of Calendula and Zinnia need darkness, so they should be covered well with soil.

Roots go down, shoots go up

Germinate some bean or gram seeds on a moist cloth until each has a small root and shoot. Tie them gently to glass plates covered with wet blotting paper: one upright in sunlight, one upside down in sunlight, and one upright inside a box that lets light in through one small hole.

After some days, the upright root grows downwards and its shoot upwards. In the upside-down seedling, the root bends and grows downwards and the shoot bends and grows upwards. In the box, the shoot grows towards the hole, while the root keeps growing downwards. So shoots grow upwards and towards sunlight, and roots grow downwards.

The Indian scientist Jagadish Chandra Bose (1858–1937) built a machine called the crescograph to record how plants respond to light, heat, electricity and gravity, and to measure how fast they grow.

Using what we know

Because seeds need water and air to germinate, grains and pulses are dried well and kept in dry, closed containers, so they do not sprout in storage. A seed that is given water and air, on the other hand, germinates and grows, which shows that it is living. Learn how characteristics like these are shared by all living beings in characteristics of living things.