Dispersal Agents 1. Impervious seed coat 3. Humidity sensitive expulsion of seeds 4. Bristles Still, dispersal is a chance event. Seed must land in an are favorable to growth, and ideally at a time favorable for growth.
Many seeds mature at a time unfavorable for growth.
Some essential condition for growth may be missing, such as warm temperatures or moisture. Dormant seeds apparently monitor the surroundings in a variety of ways, chemical, mechanical and temporal. For some, the seed coat must be exposed to abrasion, to physically wear it away. Others undergo changes in hormone concentrations, notably abscisic acid and gibberellins. Many seeds break dormancy in response to environmental triggers such as temperature changes, fire, drought or light exposure.