ABSTRACT
Dormancy is a property of many weed seeds that enables them to survive conditions hazardous to plant growth and to germinate at some later time or in some other place. Originally, nondormant seeds and seeds that have had their primary dormancy broken may pass into secondary dormancy if their germination is inhibited under certain conditions. This chapter describes germination as the resumption of embryo growth sufficient to result in protrusion of a portion of the embryo through all coverings over the embryo. In many weed seeds, dormancy is imposed by coats or coverings over the embryo. These coverings may prevent germination by: blocking water entry to the embryo; limiting exchange of respiratory gases; blocking light penetration to the embryo; mechanically constraining embryo expansion; and/or preventing loss of inhibitors from the embryo. Chemical manipulation of weed seed dormancy and germination in the field is one method by which weed seeds may be made more susceptible to weed control methods.
