Germination is usually the growth of a plant contained within a seed; it results in the formation of the seedling. It is also the process of reactivation of metabolic machinery of the seed resulting in the emergence of radicle and plumule. The seed of a vascular plant is a small package produced in a fruit or cone after the union of male and female reproductive cells. All fully developed seeds contain an embryo and, in most plant species some store of food reserves, wrapped in a seed coat. Some plants produce varying numbers of seeds that lack embryos; these are empty seeds which never germinate. Dormant seeds are viable seeds that do not germinate because they require specific internal or environmental stimuli to resume growth. Under proper conditions, the seed begins to germinate and the embryo resumes growth, developing into a seedling.