Germination
Germination is the beginning, or resumption, of growth. It is a term generally used in relation to seeds, but can equally refer to other structures such as buds or fungal spores.
In seeds, germination occurs when the embryonic plant inside the seed sprouts and pushes out through the exterior coat of the seed.
There are two basic types of germination; hypogeal and epigeal.
Hypogeal germination
The first step in hypogeal germination is that the tiny, embryonic root (the “radical”) pushes out through the bottom of the seed so it can start to take up water and nutrients. Next the stem of the plant pushes up through the soil with the first true leaves at the tip. The true leaves then open and photosynthesis can begin to provide the growing plant with energy. The seed leaves (called cotyledons), which usually store the energy to power germination, are left below ground.
Plants whose germination is hypogeous include:
- Sweetcorn/maize (Zea mays)
- Pea (Pisum sativum)
Epigeal germination
The first step in epigeal germination is the same, ie the root pushes down and out of the seed to start drawing up water and nutrients. Then the stem pushes upwards, but in this case it pulls the seeds leaves (cotyledons) above ground. This is why the first leaves you see on seedlings are sometimes different in form to the ‘normal’ leaves for that plant. The true leaves then open further up the stem and the seed leaves eventually wither and fall off, their job done.
Plants whose germination is epigeous include:
- Garden bean (Phaseolus vulgaris)
- Onion (Allium cepa)
