Gymnosperms are plants that produce uncovered seeds in a cone. Conifer trees such as pines, firs, spruces, and balsams are all gymnosperms. Cone-bearing plants reproduce by making seeds in their cones. Pine trees, like other gymnosperms, actually have two kinds of cones—a female cone and a male cone. Both are made up of scales arranged around a central axis. But each one is a bit different due to its particular function. The female cone is the structure typically thought of when referring to a pine cone.
The male cone on a pine tree is smaller and softer than the female cone. Male cones grow in groups on the end of twigs. The male cone also has scales, each of which bear two pollen sacs. In the spring or early summer, these sacs open and release their grains of pollen. Each grain has two air bladders on it, aiding in its dispersal. When a grain falls onto a female cone, the reproductive cycle begins. From start to finish, the cycle takes over two growing seasons.
The female pine cone is attached to the branch by a stem, or peduncle. The peduncle continues through the entire length of the cone forming the rachis (axis). Scales grow along the length of the rachis in a helical fashion. These scales overlap each other like fish scales. Pine cones have two types of scales. The first is the umbo, which is the first year's growth. The second part grows in the second year after fertilization. It is called the apophysis.
Female cones grow upright on the ends of branches. When pollen grains are released from the male cone, some get between the scales of the female cones. On the upper side of each scale are two ovules. When the pollen reaches an ovule, the egg is fertilized. An embryo begins to grow, protected by sporophytic tissue. The developing seed takes over a year to mature. By maturity, the cone has turned brown and hardened around the developed seeds.
Distributing the Seed
The scales on the cones of some species flare out when fully developed, at times releasing the seeds. Most cones fall to the ground when the cone matures, at times with the seeds still in the scale. Some pine cone seeds have wings attached to the seeds to aid in their dispersal. Others, though, are wingless. Some species of cones stay closed and attached to the tree for many years. These may only be opened through rotting, by animals looking for food, or fire.