| Abstract: | The development of the gametophytes and fertilization of Pseudotaxus chienii Cheng has been investigated. Pollination first occurred on April 17 (1964). The pollen grains shed at the uninucleate stage and germination on the nucellus is almost immediate. The pollen tubes approached the freenucleate female gametophyte about May 5. The spermatogenous cell is continuously enlarging with the growth of the pollen tube and two unequal sperms are formed after its division. Occasionally the small sperm may divide further into two smaller ones. During pollination the megaspore mother cell is in meiosis and 3 or 4 megaspores are formed. Generally 2 or 3 megaspores at the micropylar end are going to degenerate while the chalaza] megaspore is rapidly enlarging. After 8 successive simultaneous divisions of the functional megaspore 256 free nuclei are resulted and they are evenly distributed at the bulge of the famale gametophyte. Then the wall formation follows. Sometimes there are more than two, even as many as 5–6 gametophytes developed within a single ovule. The archegonial initials become differentiated at the apical end of the female gametophyte. They are usually single and apical, rarely lateral in position. The number of the archegonia vary from 3 to 7, usually 4–6. There are 2–8 neck cells in each archegonium which is surrounded by a layer of jacket cells. The central cell divided about May 20–26 (1964) and the division of the central cell gives rise to the egg and the ventral canal nucleus, the latter being degenerated soon. There are many proteid vacuoles near the nucleus of the matured egg. The fertilization took place about May 23–26 (1964). At first, the pollen tube discharges its contents into the egg, then the larger sperm fuses with the egg nucleus in the middle part of the archegonium. At the same time the male cytoplasm also fuses with the female cytoplasm and a layer of densely-staining neocytoplasm is formed around the fused nucleus. The smaller sperm, tube nucleus and sterile cell usually remain in the cytoplasm above the egg nucleus for some time. Based upon the observations of the development of the gametophytes and fertilization the authors conclude that Pseudotaxus is more close related to Taxus than any other member of Taxaceae. |
