Gymnosperm sporophytes produce reproductive structures called cones or strobili. In cycads, male and female cones occur on different plants, but a single pine tree has both male and female cones. Sometimes the reproductive structures do not look like the typical pine cone. For example, junipers and yew trees have modified cones that resemble berries. Cones also vary in size. Male cones are usually smaller than the female cones of the same species, and the cones of cycads are considerably larger than the cones of conifers. Cones also differ in their attachment to branches. The female cones of fir trees of the genus Abies extend upward into the air from the top side of a branch, while the cones of spruce and Douglas fir droop downward.
The typical male gymnosperm cone is a modified branch in which a central stalk or axis has modified leaves called bracts attached to it all along its length. These bracts, called microsporophylls, serve as sites for the development of microspores, which are one of the two types of spores that gymnosperm sporophytes produce. The development takes place on the inner surface of the bract in structures called microsporangia. Inside these structures, cells called microsporocytes develop, and these microsporocytes produce the microspores by undergoing a type of cell division called meiosis. These microspores then germinate and produce the male reproductive structure known as pollen.
The typical female gymnosperm cone is also a modified branch similar in structure to its smaller male counterpart. Its bracts, called megasporophylls, contain megasporangia in which megasporocytes undergo cell division and produce megaspores, the second of the two types of spores that the gymnosperm sporophyte produces. When a megaspore germinates, it develops into a female reproductive structure called a megagametophyte, in which a number of eggs develop.
The megagametophyte and the pollen produced by germinating gymnosperm spores constitute the sexual gymnosperm generation. Wind blows pollen from the male cone to the female cone. The pollen produces sperm that fertilizes eggs, which in turn develop into seeds. Most of this development is a function of the sexual generation, but the entire development takes place within the microsporangia of the sporophyte. Besides, the sporophyte contributes protective coverings. A structure called a nucellus, composed of sporophyte tissue, surrounds the megagametophyte, and an additional sporophyte covering called the integument provides additional protection. The seed coat is also sporophyte tissue. Unlike flowering plants, the sporophyte does not provide an ovary for seed development, nor does it enclose its seeds in a protective fruit. For this reason, gymnosperm seeds are called "naked seeds."