What causes a seed to grow?
What is germination?
When a seed does not germinate immediately after leaving the parent plant, it goes into a period of dormancy or inactivity. Dormancy is sometimes required for a seed to be viable. A seed can sometimes stay in a state of dormancy for years. In order for a seed to come out of this dormancy state, conditions have to be ideal. Ideal conditions depend of the seed type but they include factors like: moisture, temperature, light and in some cases even fire. For example, the seeds of the lodgepole pine are only released from the cone after being exposed to fire. Germination is when a seed "wakes up" and starts to grow. Some seeds need complete darkness to germinate, while others need to germinate in the light.
Dormant seeds contain less than 10% water making them very dry. This enables the seed to be preserved and survive to the time of germination. At the time of germination a seed begins to absorb water and it begins to swell. Also the seed will begin to use its own food storage contained in the endosperm. The seed coat will split and the radical will emerge.
Source: Discovery Channel