CK-12 Foundation
Ck 12: Biology: Plant Responses
[Free Registration/Login may be required to access all resource tools.] Describes ways that plants respond to environmental stimuli.
NC State University
Horticulture Information Leaflets: Overcoming Seed Dormancy: Trees and Shrubs
Good list of examples of how dormancy in tree seeds can be overcome. In the discussion, you'll pick up a fair amount about dormancy in plants.