Types Of Seed Germination - Epigeal and Hypogeal

I wasn't going to mention the types of germination, but if I ignore it someone is bound to point it out. Whilst this has little or no effect upon growing techniques, it does give a more complete representation of the germination picture. As we shall see (hopefully), following the emergence and establishment of a new root system (radicle), the stem starts to develop and the plumule is thrust upwards. However, there are two types of germination, dependent upon what happens to the cotyledons: i.e. whether these grow ABOVE the ground (epigeal) or remain BELOW it (hypogeal).

EPIGEAL GERMINATION ('epigeal' means 'above the ground')

In dicotyledons, if that part of the shoot axis just BELOW the cotyledons (the hypocotyl) elongates, this drags the cotyledons out of the soil (the hypocotyl bends over and drags the cotyledons behind it). The plumule, along with its delicate growing point, the shoot meristem, is protected by being enclosed between the cotyledons. e.g. Most seeds, including sunflower, castor oil and French bean HYPOGEAL GERMINATION ('hypogeal' means 'below the ground') If that part of the shoot axis ABOVE the cotyledon(s) (the epicotyl) elongates, the plumule still emerges from the ground, but the cotyledon(s) is/are left behind. The epicotyl is also hooked and the plumule is dragged backwards to minimise damage to the tip. e.g. Broad beans, peas and corn. In both cases, the shoot straightens upon reaching light. This is another phytochrome-controlled response. See also: 'Hypogeal Germination of Monocot Corn (Maize)'; 'What Is A Seed?'; 'How To Germinate Seeds More Successfully'