The seed contains the embryo of the new plant, with a supply of food for the embryo until it has formed sufficient roots and leaves to obtain its own food. The food, endosperm, may be in the seed leaves or it may be outside the seed leaves and be absorbed when the seed germinates. To start germination, the seed leaves absorb water and swell, and the radicle emerges, followed by the plumule. For some seeds, their future germination response is affected by environmental conditions during seed formation; most often these responses are types of seed dormancy.
Water - is required for germination. Mature seeds are often extremely dry and need to take in significant amounts of water, relative to the dry weight of the seed, before cellular metabolism and growth can resume.
Oxygen - is required by the germinating seed for metabolism
Temperature - affects cellular metabolic and growth rates. Seeds from different species and even seeds from the same plant germinate over a wide range of temperatures. Seeds often have a temperature range within which they will germinate, and they will not do so above or below this range. Many seeds germinate at temperatures slightly above room-temperature 60-75 F (16-24 C),
Light or darkness - can be an environmental trigger for germination and is a type of physiological dormancy. Most seeds are not affected by light or darkness, but many seeds, including species found in forest settings, will not germinate until an opening in the canopy allows sufficient light for growth of the seedling.