Abstract
All conifers are wind pollinated but show tremendous variation in pollination mechanisms, pollen development and sperm structure. Differences in sperm and egg structure and the fertilization process lead to variation in cytoplasmic inheritance. Four types of male gametophyte development occur. Historically several terminologies have been used. A standard terminology is used here. The simplest development occurs in the Cupressaceae and Taxodiaceae. The microspore divides forming a tube cell and a spermatogenous cell. The latter forms two large sperm cells with zoned cytoplasm and many organelles. In the Taxaceae and Cephalotaxaceae the microspore divides to form a tube cell and antheridial cell. The antheridial cell forms the sterile cell and a spermatogenous cell. The latter forms two equal-size sperm nuclei and the spermatogenous cell cytoplasm degenerates. In the Pinaceae the microspore divides unequally to form a small primary prothallial cell and a large central cell. The latter divides to form a second prothallial cell and an antheridial initial. This divides to form a tube cell and an antheridial cell. The antheridial cell divides to form a sterile cell and a spermatogenous cell. The latter divides forming two sperm nuclei that remain within the spermatogenous cell cytoplasm while in the pollen tube. In the Araucariaceae, and possibly the Podocarpaceae, development is similar to the Pinaceae except that the primary prothallial cells divide forming many secondary prothallial cells or nuclei. The spermatogenous cell nucleus undergoes mitosis in the pollen tube forming two sperm nuclei that incorporate large amounts of spermatogenous cell cytoplasm.