Animation 27.1: Life Cycle of a Conifer

INTRODUCTION

Firs, cedars, spruce, and pines rank among the great vegetation formations of the world. All of these trees belong to one group of gymnosperms—the conifers, or cone-bearers. Gymnosperms derive their name (which means "naked-seeded") from the fact that their ovules and seeds are not protected by ovary or fruit tissue.

In conifers, the same diploid sporophyte plant has both pollen-producing strobili and egg-producing cones. Most conifer ovules—which, upon fertilization, develop into seeds—are borne exposed on the upper surfaces of the modified branches that form the scales of the cone. At maturity, the scales of the cones separate, and the seeds are released into the air to be carried sometimes considerable distances by the wind.

CONCLUSION

Conifers have cones, but no motile cells. Like most seed plants, the conifers do not rely on liquid water for sexual reproduction. Instead, wind assists conifer pollen grains in their first stage of travel from the strobilus to the female gametophyte. The haploid gametophytes develop partly or entirely while attached to and nutritionally dependent on the diploid sporophyte.

The seeds of gymnosperms are complex and contain tissues from three generations. The seed coat develops from tissues of the diploid sporophyte parent (the integument). Within the megasporangium is the haploid female gametophytic tissue from the next generation, which contains a supply of nutrients for the developing embryo. In the center of the seed is the third generation, the embryo of the new diploid sporophyte. The seeds of some species may remain viable (capable of growth and development) for many years, germinating when conditions are favorable for the growth of the sporophyte.

Textbook Reference: Key Concept 27.2 Once Dominant Gymnosperms Still Thrive in Some Environments