Conifers, which include cedars, pines, spruce and redwoods, are gymnosperms. Their needle-like leaves lose water slowly. This allows conifers to keep their needles during periods of extreme cold, such as winter, when water is scarce. Gymnosperms include the longest-living organism on earth (a 5,000-year-old bristlecone pine), the tallest (a 115-meter-high coast redwood) and the largest in volume (a giant sequoia with a volume of 1,540 cubic meters).
Gymnosperms and Angiosperms
Gymnosperms differ from angiosperms, or flowering plants, in having exposed seeds. Think about the seed in a cherry or peach. The cherry or peach seed is enclosed by fruit; apple and cherry trees are angiosperms. The seeds of a gymnosperm are produced in the plant's female cone. When the seeds mature, they are released as bare seeds to drift with the wind, fall to the ground and germinate.
Male Pine Cones
Male pine cones are smaller than female cones and only live a few weeks. You can identify them as brown, tube-like clusters on the branches of a pine. The cones that make up these clusters contain scales, or microsporophylls, around a central stem. Each scale holds a pollen sack, or microsporangium, and each pollen sack contains pollen grains, each called a microgametophyte, or microspore. Through mitosis, microspores in the male microsporangium become male gametophytes, which are commonly known as pollen. The male gametophyte has two air bladders that will help it float on the air when it is released by the male cone. In some conifers, male cones are higher in the tree than female cones, allowing the pollen when released to take advantage of this added height in floating farther when the wind or breeze carries it off.
Female Pine Cones
Female pine cones are probably what you think of when you think of a pine cone. They live for several years, unlike male cones, and are larger than male cones. Often you'll find female cones lower on the tree to take advantage of the downward fall of pollen. Like male cones, female pine cones have scales, but these scales are much more prominent and are called megasporophylls. The scales are also oriented around a central stem. Also like male cones, the female pine cone has a sporangium structure, referred to as a megasporangium. Through mitosis, a female megaspore in the megasporangium becomes a female megagametophyte. Each megagametophyte then produces one or more structures called an archegonium, each of them with an egg inside.
Gymnosperm Life Cycle
When the male pine cone releases its pollen, breezes and winds carry the pollen to another pine tree. Here the pollen can become caught between the central stem of the female cone and a megasporophyll. This is pollination. The pollen then produces a pollen tube, which grows into the female megasporangium, also called an ovule. The process can take over a year. When the tube has formed, sperm moves down the tube from the pollen to the female egg. This is fertilization. The fertilized egg will produce an embryo. The embryo will be enclosed in a seed case made up of part of the megasporophyll. The seed case will have a small wing that will help the wind disperse it effectively. As soon as the seed is mature, the female cone will open to release it. Many pollen grains pollinate and fertilize many female eggs at the same time in a female pine cone.