It can happen naturally as in the intestine of an animal or artificially by etching the seed with acid or mechanically rubbing off the seed coat E. Cold Period 1. After being hydrated , the seed needs freezing or near freezing temperatures for a certain minimum time 2. This certain minimum amount of time at this cold temperature signals the seed that the winter is past and it can germinate without being frozen by frost or cold weather 3. This happens naturally with most wild seeds that are in the ground over the winter. They become hydrated in the fall and go through the winter and germinate in the spring as a result of experiencing the cold temperature.
Stratification is an artificial method of giving seeds a cold period.
The seeds are spread out on wet cheese cloth. The sheets of cheese cloth are stacked on top of one another and placed in a dark cold refrigerator for approximately two months depending upon the species. The wet cheese cloth hydrates the seed and the cold period makes it ready to germinate. These must be leached out of the seed before it will germinate. G. Heat or Fire - Cones of certain of the pines remain closed after the seeds become mature.